I just brought my used 2001 GS 430 home on Friday. Looked like the engine bay had been detailed in the last six months buy someone with a whole can of armor-all. Wow - does that slimey stuff attract dust and dirt. This morning I just washed it with dish soap (would normally use a more mild car wash) but it was a greasy mess. Now it is cherry! Like new. I have been using car wash soap for years on my Corvette and other cars engines. Never had a problem. I use a garden hose and don't mess with covering the electronics - Quality of this Lexus stuff is very impressive - If I have not had problems with my Chevy or Olds - certainly won't with this.
I would avoid strong degreasers (dish soap is pretty strong) - I think it may suck oils out of the rubber parts and may promote dry rotting??
