I use COMMA HYPERCLEAN on engines/grease/muck etc. brush on rinse off with water/brush. They come up really good and spangly it has inhibitors and stuff in there that nip rust and leaves a film protection for ferrous stuff like nuts/bolts, this method allows full control of the application, brilliant stuff.
Like yesterday i removed the glovebox and the vent hose behind it on a mk2 and found a mouse had been storing food in the vent pipe so after shaking out the peanuts etc. i still had a washing up bowl of about 5%HYPERCLEAN/95%water that i had cleaned the air filter sponge of old filter oil with and while it was drying i just used the remains to clean the hose and the glovebox which both came up like new.
I buy it by the gallon it is @ £12-15 quid, cleans everything, oh yeah the remaining bowl contents were then used to clean all the wheels/tyres on the van.
I'm off out now to refit the hose/glovebox and will decant through a funnel and store the bowl mixture remnants in another sealed container for future use. Reckon i used about 1/2 litre for this lot so cost is say £2.
In fact i might whip off the other vent hose on drivers side first as the critter may have nipped across the blower and put a stash in that one.

Must renew the scuttle intake mesh.