Removing primer and stonechip overspray from painted panels

[Colin Lindsay]

I've dug out and refitted the Herald Estate rear door from where it's been propped against a wall for twenty years - it was professionally sprayed in two-pack back in 2003 but I've noticed some considerable areas of overspray due to me working on other things in the vicinity. It's a lot of grey spots so possibly primer, possibly stonechip, but covering an area of about six to eight inches on the flat face of the door and rough to the touch. It's not responding to picking off, plastic scouring pads, or petrol. Before I do anything that will take all the paint off to the bare metal all suggestions as to techniques or products are welcome. 

[chrishawley]

As a rescue procedure one approach to dealing with overspray is to 'block' the affected area with wet'n'dry. 400-600 grit initially, then 1000-1200 grit to take our the score marks, then a severe polish with a electric mop with something like Farecla G6 or equivalent. But if it's 20 year old 2k even heavy mopping may not have a full effect in bring up the paint to a nice gloss finish.

Could work but possibly ends up being more effortful than just flatting and keying the whole panel and applying new paint (but subject to other considerations such as texture and colour match to the other panels on the vehicle.)