Marine Clean works good, I have used a lot of it. I always mix it 50/50 but you can go with a lighter mix. think the paper work/directions I got from the POR distributer/dealer says you can mix it as low as 10% ratio.
Be careful on aluminum (maybe it`s may 50/50 ratio) it will discolor it some if left on too long. I spray in on the oily parts of the engine now and then as a touch up, and use the garden hose with a sprayer nozzel and wash it off.
I have a place on the low side of the driveway I wash the cars. I use the Marine Clean and a stiff brush to scrub the wheels/tires. I have noticed the MC does attack the Asphalt. Asphalt is just a tar and gravel mix, and a petrolium product. the MC emulsives the oils. best to use it over concrete.
If you can steam clean the engine and the eng/bay it will save a lot of elbo grease. when we got the 240 3 yrs ago, the eng was a greassy mess. I steamed cleaned it, then using wax grease remover.......
and a bunch of rags, wiped down everything, and followed up with a wax with a paint cleaner. came out looking like new.
Charlie