My radiator has a leak in the lower left, my indie said its an old leak but needs to be sorted ASAP. I have a 3 month warranty with Warranty wise but it doesn't cover the radiator. Also he has advised me that my front diff is possibly porous as its leaking through the casing.

This was bought from a trade seller who got it straight from a main dealer do I have any rights to contact him considering I have only had it 4 weeks?

You have a right to contact him - but whether you can demand he does anything is less likely.

Warranties tend to cover things that have failed rather than 'just' leaking.

I'd contact the seller, tell him what you have found, that you are unhappy and see what he says.

Have a look at the Consumer Rights Act 2015/the Citizens Advice summary - 30 day right of rejection plus other remedies, might be useful in dealing with a trade seller, unless 'sold as seen' or similar applied to the deal. Only Range Rovers since 1988

There was no sold as seen receipt but I'm sure I've read that does not mean anything any way? Trouble is if I email him he probably won't respond.