In general, I tend to muse Humbrol Model filler, although Humbrol have had stability problems, where the binder comes out of solution. However, leaving the top off the tube for 24 hours allows it to thicken up to a usable consistency.
It's like the little girl; when it's good, it's very very good...
Recently, I have used superglue with a fair degree of success. the secret is to sand it before it gets too hard - it eventally sets harder than the styrene!
For hairline cracks and pinholes, correction fluid works well, particularly iff you can get the solvent-based kind. It flows int the crack, solidifies in a few seconds and is easy to sand.
Hope this helps
Colin
Gentlemen! You can't fight in here; this is the WAR ROOM!