Yeah, acetone takes Mr.Surfacer off too... I don't know how/if it affects airbrush tho (o-rings and stuff).

Which reminds me of another one:

When i have to cover small gap i cover it with Mr.Surfacer and when it dries i wipe the excess with q-tip soaked in acetone. Be careful tho because acetone can melt/damage styrene - don't stop in one place and don't force it... This way you don't have to sand...

Cheers!