CRC Heavy Duty Degreaser, 19 oz Aerosol Can, Clear

Q: Can you use under engine oil pan area

Yes, it will easily clean up grease and oil! Drys fast also!

Q: does it take off wax film on metal to be painted ?

Not sure, acetone would be a better choice.

Q: is crc heavy duty degreaser non-flammable

It has a fire hazard rating of 1 (will flash at or above 200 degree's) but if you want a good grease cutting solvent that leaves no residue the CRC heavy duty degreaser is the right choice

Q: Is this product safe for older plastics? I assume it's not.

To be perfectly honest, I'm not sure if it is "safe" for older plastics; then again, I'm not certain what you mean by "older." I assume you're concerned about corrosion or some other chemical reaction with those materials. It does say "non-corrosive" on the can and is safe for use in machinery that processes foods (again, according to the can), so I would imagine you would be OK to use it on plastic. Suffice it to say, I have yet to encounter any detrimental issues using this product on any of my tools, may of which were inherited or otherwise second hand and made from a wide variety and age of materials.