Found this can of unopened supplement
1#1052367
can says GM ENGINE OIL SUPPLEMENT (concentrate)
is this break in oil or stuff like the old STP.

 

Apparently the old formulation is quite good, with both zinc and moly. The new stuff, less so. Found this from 2004:

 

I used to sell that stuff back in the 60's when I worked for a Buick dealer. Really good stuff.

 

The EOS worked very well, used it with new cams, lifters etc. and to quiet old ones.

Top Engine Cleaner 1050002 was also fantastic. Got introduced to TEC after tuning and briskly test driving a '69 Chevy small block that started to knock. Old school service manager listened to it and said he thought it was carbon on top of a piston and to try TEC. It worked, crisis averted.

 

The GM engine flush was also really good. The new EOS still has reasonable levels of ZDDP, I think it tested at about half that amount. Surprisingly enough we bought some of these products while working at a Ford dealer. Ford's glass cleaner was horrible, GM's was quite good.

 

I use 1/2 bottle of EOS with Delo 400 CI4+ oil (old spec, not meeting CJ) in flat tappet engines with high spring pressures and cam lift rates.

 

I use a full bottle of EOS and 4.5 qts of non detergent straight 30w to break in a FT cam and lifters.

 

I like Comp 159 for break in, However, moly lube on the cam, lifters, and additive will plug the oil filter so don't run them more than the 20-30 minutes break-in time. The old formula EOS doesn't seem too bad that way.