A good metal filled epoxy will do the job well. Check out some of the Devcon products. 

As for not causing a problem I have fixed many an overheating problem by fixing this area. If engine out for major repair I get it welded. 

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Brett Ne
Sent: Friday, September 26, 2014 2:28 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Coolant Pump: wear at case

If I were to use some kind of epoxy to rebuild the missing metal, I would drill a number of shallow holes at an angle using a tiny drill bit to give the epoxy a good secure bite into the base metal.  In addition, I would mix in some fine glass fibers with the epoxy to help keep smaller chunks from cracking  apart and flowing through the cooling system.

That said, I don't think that I'd bother messing with it.  I think that the only way you'd see any significant loss in cooling capacity is if the gouging is continuous from the outer portion of the housing to the inner portion, which would allow pressure backflow into the input portion of the impeller.

--
Brett in Portland, OR
"Albert" '82 VanaFox I4 Riviera