Sorry to hear you've been through this too Stuart. Seems a lot of TDV8 owners have...

I will report back how i get on with a repair. If it weren't for the poor access i'd be replacing the manifold in a heartbeat. 2008/58 FFRR 3.6 TDV8 Vogue

3,000 miles later i can report that the 291i is holding strong. I roughed up a large area with 80 grit paper, and cleaned meticulously with degreaser then IPA solvent. Applied the sealant in 2 goes, quite thick and worked it in as best i could. I applied a large area - around the size of my hand to cover a small crack so that probably helped.

In the end i didn't use the sika primer/activator. 2008/58 FFRR 3.6 TDV8 Vogue