I feel your pain.
I have a 96. Optispark and all.
Engine had NEVER been cleaned since new.
Lots of dirt, grime, sand, etc under the hood.
Started out with a cotton rag. Wiped off all the surfaces and hoses. Then hit it with air compressor. Then the rags again. Then air again.
THEN magic happened.
Product is called Trim and Shine.
Made in Poplarville, MS.
Sprayed that on all plastic and rubber parts and with no scrubbing, it makes them look brand new!
The underside of the hood and the wheel wells were done with Castrol Super Clean and more rags. Boy was that filthy, Those rags never came clean, they are now in the trash. After a few treatments with the Castrol purple bottle. I hit the underside of the hood with STP son of a gun foaming Tire Cleaner. Spray it on, let it activate and start running. Wipe off with more disposable rags before it drips on the ground or wheels.
Have underside of the hood looking this it was repainted!
I have only started on the engine bay with one cleaning. PUlling wheels when i get in new garage and really getting it clean in there!
Rain
Pics:
http://www.rainontheinternet.com/adaturing/june03vetteshow/
Wish i had taken some before pics! It was BLACK In there.
Good luck