I think that there is some misunderstanding here as to how oil stop leak products work. They are not like radiator stop-leak products, and they won't interfere with oil flow through the engine.
Oil stop leak products work by softening and swelling the oil seals, like the cam seal and the front and rear main seals.
This shortens the life of the seals, so if the car is high mileage and ALL the seals need replacing or you know the car won't go much further anyway, no harm.
I would hate to see you shorten the life of good front and rear main seals to slow a leak at the cam shaft seal that could easily be replaced at the next timing belt replacement.
If part of the problem is the valve cover gasket, spend $10 and do that yourself. Also, put cardboard or a drip pan under the car if you park it inside. Like the man said, you can buy a LOT of oil for $700.