Alot of people swear by SF doing all kinds of great things in the fuel system. But from what I've read over at
Bob Is The Oil Guy theres no documented proof of it doing anything in the crankcase besides thin out your oil. Its a solvent and not good for your seals.
On a Saturn forum I belong to they all recommend doing a MMO soak (marvel
mystery oil) by pouring MMO into the cylinders and letting it sit to help break up the ring coking. Others have had success I wasn't so lucky. I did the same with SF same results. White smoke.
Auto-rx on the other hand has helped immensly.