[Teflon]

It's unlikely to help with the greenery, but once you've got the car nice and clean, for future maintenance I find the best solution is a set of makeup brushes from the local pound shop. Much cheaper than dedicated "detailing" brushes, but do just as good a job.

For the green mould, I would try giving it a good soaking with a pre-wash (snow foam or similar) to soften it up, then follow with a paint brush fully loaded with a good quality apc. As you've already discovered though, be careful with the paintwork.

Cliff