what rear diff oil on my 02 sti type uk,and have been reccomended syntrax for gearbox is that ok to use ?also running about 330 bhp so shall i use 5w/40 or 10w/40 in the engine. i know this has probably been asked 10 million times but want the best in it,cheers

 

The Syntrax (Driveline) will be fine in the rear diff.
For summer use I'd say 10w/40 most of which are semi-synthetic although Millers and Motul do full stn. versions of that grade.

JohnD