Hi Flix, thanks for coming back to me! I took the plunge and went for it (with my wife's help, who's much handier with a paint brush than i am) - thought i'd post just in case it's of any help to anyone else in the future, as Thunderwing's a g1 figure that's a) in demand, b) horribly expensive, and c) prone to paint chips.
I got a set of new stickers for the figure from Reprolabels - the set includes all labels for both the inner and outer robot, including stickers that would have been factory applied on the original toy. The labels aren't Reprolabels' best work - they're a little thin and use dot spacing for grey shading rather than the solid block colours of the original labels - but they still brighten up the figure no end. (Not knocking the company by the way - i ordered some labels for a g1 sunstreaker as well, and they were absolutely indistinguishable from the originals.)
The paint had chipped substantially from the black head crest, the black squares in the top corners of the chest area, the black stomach section, the black piping on the legs, the gold piping around the waist, and the large green sections on the flanks. All paints used were Games Workshop/Citadel acrylic paints. We applied the paints straight on - no primer or abrasion of the surface in order to provide a key for the paint. As the original paint was still partially in place, I painted over the whole sections rather than trying to 'touch up' or strip all the original paint before applying. The black sections took two coats of chaos black, the gold detailing took three coats of shining gold, the green took a couple of coats of a mix of snot green (charming name) with a drop of moody blue.
I've posted a photo below to give an idea of the results - i'm pretty pleased. The gold particularly has come out spot on. The green mix is slightly less vibrant than the original paint colour, but i'd defy anyone to notice without putting two figures side by side. The black is... well, very black. None more black, as Nigel Tufnel might say. The finish is a little more 'matte' than the original, but this is only really noticeable in direct light.
There's a photo below of the toy in robot mode - I should probably have taken a 'before' shot as well, but i, um, forgot...
http://farm3.static.flickr.com/2428/363 ... 3a.jpg?v=0Anyway, hopefully this all might be of use to someone out there.
Cheers