In reply to doz:
> Removing the glue with a heated scraper (Colltex do one) is definitely the easiest way and avoids getting everything including yourself covered in old glue/heather/ptarmigan poo etc
Actually I find that the using some old bedlinen strips is the easiest and least messy method. Simply place fabric strips on the glue-side covering it. Heat with and iron and rip the strip and place in garbage bag. Two runs is often enough to get an almost clean results, the apply new glue and call it good.
As for the OP. If there are no holes in the glue (just some globs etc.). It is often enough to "borrow" wifes tweezers and pick out all the visible crap from from the glue (remember to buy new tweezers or face her wrath). Then using a sticker backing paper or parchment paper, re-distribute the glue evenly using a waxing iron.
If there are small patches without glue, then get some glue (in a bottle, e.g. BD do one) and fill the patches. And after that glue has settled, do the re-distribution.
If the whole glue is a lost cause (big patches and globs, full of crap and not sticky anymore). Then remove completely (or almost completely, see above). And re-glue with those transfer sheets. But don't bin the backing paper and instead use it the next time you need to fix the glue...
Oh, and wax yer skis properly.
In essence, you only need to get new skins, if you change yer skis and the skins are way too small... or that you've mistreated them and ripped too many big gashes on 'em... Or you've simply worn through them (not enough hair left, so don't really grip anymore). Glide, use BD glob stopper... or any ~0 to -5C parafin... the same stuff you put on yer skis. Albeit don't hotwax the skins, simply rub it on. Stops the skins from gettin' all wet (or at least they get less wet), so stay on better. Also they'll glide better.