Hello!
A few weeks ago I got a lovely G1 Bowtie off of Ebay, and she is in wonderful condition apart from some brown marks/stains on her side and leg.
I haven't tried anything to remove them yet, as I have never had this problem before and don't want to do anything to my favourite pony that might damage her
these are classic pony age spots. they're a very common problem in g1s. the only known way to remove them is sunfading with salon 40 cream. the MLP preservation project @StormMaeker linked is the best restoration resource around, so definitely check it out if you want to tackle trying to remove bowtie's spots.
Oh no--that looks like it could be the start of pony cancer. It is extremely difficult to remove those spots, it will take a lot of patience and time, the right supplies. I third the advice given in the Pony Preservation Project to try and restore her.
Small update: I gave her a little wash with some soap on a cotton swab and the spots seemed to fade a little? Which has lead me to think that maybe they are just some suspicious-looking surface stains, but I will keep an eye on her and check out the Pony Preservation project again later
