If you are a "rough old Bast**d" like me you do the following..
- Run the car around till its nice and warm
- Open the bonnet while it is still running
- Attack with a steam cleaner
You will be amazed at the results.
Do avoid direct "blasting" of the distributor.
Use a steam cleaner, one that generates heat as well as pressure, rather than just a pressure washer.
THis is my standard method of attack on the rally car after competing in stages, never had a problem, except that the windscreen sometimes steams up
Standard practice in garages when the "punter" isn't looking (sorry)
Malc