gap filler?

[nachoman]

First choice - to get the corners to line up square in the first place. And since that isn't always possible considering casting defects, warped pieces, etc, my second choice would be to glue in little slivers of styrene into the gaps using solvent cement (or laquer thinner) then cut and file to shape. Thin cracks I use a tube of auto body spot filler. The problem with the body filler is that if the gap is too wide, it's both hard to blend so that it is not noticeable, and it tends to fall out of the gap over time.