My gearbox went into limp mode and my gearbox specialist has given me two options. A full rebuild which I will do eventually, or an oil and filter change as a temporary measure so I can get my mot etc.

He said there were lots of metal filings in the oil which had blocked up the filter and caused the car to go into limp mode. Even during limp mode the car drove normally and gears changed smoothly until the oil is heated up and the car sensed no flow of oil and triggered the ECU to shut down the gearing.

So I have told him to change the filter and oil to see what happens, and I will book it in for a full rebuild when I see the symptoms come back.

I know it is a tough one to guess, but how long do you think I will have before the gearbox fails again?

Is it usually a sudden thing or a gradual slipping of gears, hesitation and thudding etc. (taking into account the gearbox has been smooth changing so far). Tom

Current Drive
2011 4.4 TDV8 Autobiography - Santorini Black - Ivory Leather

Previous Drives
2004 Model Vogue Td6 (Touchscreen) - Java Black - Parchment Leather
1994 RR Classic 3.9 V8 Soft dash - Niagara Grey - Grey Leather
1972 Series III SWB Safari - Green (Hand Painted) - Black Plastic

The aluminium filings in the oil indicate the torque convertor lock-up clutch friction plate is seriously worn allowing metal to metal contact in the clutch. As a minimum you need a new/re-manufactured torque convertor fitted. The aluminium filings also block the oilways in the oil cooler resulting in reduced oil flow thro it with the oil running hot and degrading. You really need to change the oil cooler.
If your oil fllter is blocked with filings to the extent the filter is blocked, which given the area of the filter, I find hard to believe, things are well on in terms of failure. Given that you have told your gearbox specialist to change the filter and oil I'd be inclined to get him to add a couple of tubes of Dr Tranny friction modifier to the gearbox. Snake oil I know but it does actually work.
How long you car will run to a failure is anybodies guess it could go 1k it could go 10k.
How many miles has your car done?

The autobox mechanic agreed that the whole thing ideally needs to be changed including oil cooler. He has done quite a few L322s and seems to know his stuff.

My car has done 135k on the original box (which seems to be pretty good compared to others) and I know it needs sorting properly but if I can buy a few weeks or a month with a gearbox service instead before shelling out the full wedge on the major works then it would be interesting to see how long it will last.

It's not as if it will cause any more damage to the box as I know it is near death's door, but if I can squeeze a little more life out of it all the better.

I might top up the box with some of Dr Tranny product if it offers any inkling of helping the torque converter live on a bit longer. So far I don't get any shudder at all so maybe it is early days of it cracking up. Tom

Current Drive
2011 4.4 TDV8 Autobiography - Santorini Black - Ivory Leather

Previous Drives
2004 Model Vogue Td6 (Touchscreen) - Java Black - Parchment Leather
1994 RR Classic 3.9 V8 Soft dash - Niagara Grey - Grey Leather
1972 Series III SWB Safari - Green (Hand Painted) - Black Plastic

135k is pretty good, I think it's fair to say you've had your monies worth.
I'd be interested to know which oil your gearbox specialist recommends for the gearbox, I've been advised that the oil recommended by LR ( Texaco ETL 7045E) isn't really upto the job and that I would be better off using a Fully Synthetic LT71141 oil instead. This is from a man that has rebuilt into the hundreds of GM gearboxes and torque convertors as fitted to the RR L322 and BMW X5's.
For the cost of the DR Tranny imo it's worth a go, can't make anything worse. BMW owners seem to swear by it. Bear in mind though it only masks the inherent problem, your torque convertor is very well worn and is due replacement.
You can only hope you are ok for a few months, just don't go too far without recovery cover.

Correct, the oilcooler is also after flushing full of metal parts, only the pipes you can flush. Best way is a complete renew of the gearbox, in the time, when the box is out, and at the recon Company, you have enough time to buildt out the oilcooler, (difficult to reach, and be carefull with the three screws), NEW!! oilcooler good prices in Internet, and after Fitting the new cooler and the flushed pipes, it is easy Job to install the box..., best wishes from Germany (third box in 212.000km) L405 SDV8 2017 + Lancia Flavia Coupe 1964 + RRS L494 3.0 SDV6 + C220CDI Convertible 2021

I picked the car up today to get it MOT'd and taxed and had another good chat with the mechanic. He also recommended the Dr Tranny (or similar anti shudder additive) and said he puts some in the torque converter when putting together a complete rebuild on all his jobs.

In his 15 years of doing rebuilds he says it definitely cuts down on the potential shudder and helps protect it from wear even when put in new boxes. Prior to his transmission company he worked as an engineer at Ford so does know the issues inside out. He also recommended servicing the GM boxes every 40k miles as a precautionary process, as it will show the first signs of an issue and help prevent a major failure.

At least the GM box is cheap to service at about £160 compared to the ZF gearbox which he said is about £400 a time due to the 6 speed complexity. Tom

Current Drive
2011 4.4 TDV8 Autobiography - Santorini Black - Ivory Leather

Previous Drives
2004 Model Vogue Td6 (Touchscreen) - Java Black - Parchment Leather
1994 RR Classic 3.9 V8 Soft dash - Niagara Grey - Grey Leather
1972 Series III SWB Safari - Green (Hand Painted) - Black Plastic