My cleaning routine is:
Wet with hot water (unless it's a SS then cool water). Anything with a mechanism like a brush N grow don't submerge in water incase they rust internally).
Spray with oxy laundry stuff
Scrub with a firm tooth brush then rinse
Shampoo and then conditioner mane and tail.
Leave them to dry. You can wrap a tissue around their neck to help the mane lie flat and I leave them sitting back on their backsides so water can drain out the tail hole.
Once they're dried any left over marks I go over with nail poliosh remover (as already said go carefully around painted areas).
Then when finished in the salon all my ponies get a ribbon to make them pretty
To sunfade cover the rest of the pony apart from the mark and leave it in a sunny window - can takes AGES but can work.
You can get a replacement tail from another pony or order hair from dollyhair and make your own.
Good luck with it I love cleaning up ponies