I purchased Deoxit D5 and F5 to clean up some vintage receivers. Had good success on a Sony. Using it on an old Sansui, I ended up with some knobs having nice resistance and other knobs feeling too loose. I used D5 first, spraying it into the pots, then moving the control back and forth a lot of times. Then I sprayed F5 in to replace the lube and again, moved the control back and forth. The bass knob on the Sansui provides very little resistance and feels sort of cheap now. And it feels totally different from the treble knob. Fortunately, the Sansui (QR-1500) was free and I don't have big plans for it. I just purchased and received a Sansui 3300 receiver which I hope becomes my keeper and ends my search. I don't want to mess it up. But upon plugging it in for the first time last night, I heard a lot of popping and cracking. I suspect the source knob is the first place I have to go. Should I use a different product than D5 and F5 for this? I have read, but don't quite understand, that the 5% of something in D5 removes something important. And that there's a difference of opinion on whether F5 is necessary or not to replace lubrication.