Linomite

I noticed a slight little build up of type metal on the pump plunger rod when I started casting this evening, and after a couple hours of casting lines this is what that build up became:

Linomite! It was enough to restrict the plunger from returning to its fullest upward position. Gotta keep an eye on this next time. I'm guessing that this happened because the pot was a bit too cool. I'll test the theory next time we cast. Otherwise, anyone out there have tips on how to prevent this?