SundanceUK

I tried to undo mine recently, just to make sure they will crack off when the belt is next due to be done, but my long breaker bar and extension will not budge them, even with my big Dewalt impact gun they will not undo, probably due to lost energy in the bar and swivel adaptor.
I saw a youtube vid by MG Lee who has done a lot of refurbing on his TF and had the same problem. He got round the issue by buying a set of Lexivon impact swivel adaptors and using a proper impact rated socket on his impact gun. I have purchased a set and will try them out next time I have the engine cover off.
This is the ebay link to the impact rated swivel adaptors.   
These should allow more energy from the rattle gun onto the bolt and help to shock it loose.

Here is a link to the impact sockets, I think the engine mount bolts are 18mm.       Sealey AK5613M Impact Socket Set Metric 13pc 1/2 Drive 10 - 24mm With Case Buy It Now