Goodness me, look, here's an excellent tip from some one in the trade by the
looks of it.

(quote)
I use a material called "Lab Metal" to fill pits and imperfections in cast
aluminium thermoforming moulds. Amazing stuff. One part aluminium putty,
comes in two
versions, regular and high heat. The high heat will take 1000 F IIRC, the
regular around 400 + F.
Not cheap, but a little can goes a long way. I get it at the local welding
supply store. Also available at the local FASTENAL store, and probably at an
industrial supplier near you.

complete with independent confirmation and link.

(quote) We use it also... before powder coating.
Eastwood Co has it online: http://makeashorterlink.com/?E2D5164EC
David

and they are both ignored completely.

(quote) I think I'll try the aluminium brazing (or maybe it's soldering) rod
first. A number of people on the net have reported success. Thanks. Joe.

Makes me larf... This is a dam good NG, lots of cleaver folk willing to part
with some tips.

best of luck, maybe it's the 'Not cheap' that put him off?