So I have this 4 speed that's absolutley covered in oil, grease etc.I don't have a pressure washer or parts washer so best options are...?
CT18 truckwash was good on my dirtbike, any good for this sort of thing? ther's an all hours car wash nearby, I could do it there to save my grass lol

Mr Muscle oven cleaner!! Spray it on and leave it for a little while, agitate with a brush then wash off.  

Hmmm, yeah the caustic soda works very well. The bellhousing would be alright but isn't some of the gearbox cast aluminium?

Flag that! I just bought some Chemtech CT14 HD degreaser today and it's sodium hydroxide (caustic soda) and alkaline salts. Says it's okay for aluminium, 83g per litre concentrate must be safe.