the good part about the Seafoam is that if you can find it, you can get multiple cans and clean different things. It can be used as a gas additive, oil additive, intake cleaner and lots. If you cant find one it sounds like you are stuck with the GM one. I checked the bottle of Seafoam that we have and it is O2 safe, so that isnt a problem. I dont think anyone has tried both of them, I bet both will work on your cars. It is probably a good idea to change the oil on both, you dont want the crud that it flushed out to clog an oil passage.
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1997 White SE with 181k miles MOBY DICK
Mods: Transmission Cooler, APC driving lights, Rice Pipe with K&N filter, mud flaps, 3.06 gearing, Pioneer DEH-6600 Head Unit
2000 Blue SE with 90k miles - Mom'* car