is it ok to buy additives over the counter and add them to the oil?
If you want to, but why would you. Motor oils have all the additives you need unless you have some very special operating conditions. Some of the over the counter additives will actually cause oil to gum or burn. Most of them would void a warranty. If your engine is worn out additives will not make it new. Leaking gaskets and seals can be fixed very temporarily with some additives but they actually are weakening the seals. These things are usually added just before you sell the car to a stranger.
The only additive to add to oil is SEAFOAM. All others are a waste of time, effort and money. mmalky
The only additive I still add at every oil change is Slick 50. I have actually inspected the internals of general aviation aircraft internals of those engines treated and those without. Its actually what it was initially intended for. It has also dropped my operating temperatures of my vehicles a good 10 degrees while sitting in the hot South Florida traffic. There is also the friend of most every diesel mechanic on the North Slope of Alaska where they leave their vehicles running 24/7 during Winter even while they sleep, Marvel Mystery Oil. Snake oil? Perhaps. You decide.
