Im getting ready to put my car up for sale but the engine bay lets it down massively,

Whats the best stuff to clean the engine bay, I was going to buy Gunk.
The bay and engine are in a state, Ive not bothered cleaning in there in the 2 years Ive owned it.

Then once degreased what product should I use to give a nice finish on the plastic covers and air box?



Many thanks in advance