My 97 lumi3.1 had that same crap on the cap when I Pulled it...at 137,970 miles... Its actually the DEXCOOL fluid... it will chunk up under the cap if it hasn't been changed in a L-O-N-G while...like 137,970...lol I did a complete flush and fill and actually used extended life fluid(looks yellow... not green or orange) and its all gone... never had a headgasket or intake problem on mine(thnk god) but Id bet a flush and fill will help... ALTHOUGH... Jeffco and Richtazz Both helped me alot with their advice and I wouldnt overlook the info they have given by any means... just my
on how I fixed it....oh BtW... Its now got 248,700 on it and still goin strong
MYX