From the same seller who provides most of blank tapes and pro-dubbed tapes for at least scandinavia noise labels, they'll gladly sell just perfect head cleaning liquid. No fancy bottles. No fancy names or promises. Just the basic liquid you wipe the tape heads (no rubber parts or such!) just like professionals do. Small brown glass bottle will last for decades even with extensive cleaning.
If one would want to be really taking care of collection, one should rewind tapes back and forth... was it c. once a year. It is easy if you collection is handful of tapes. If it's several hundred or thousands, I can guarantee nobody spends their days with routine rewinding process to keep magnetic tape in better health. I have broken duplicator which is meant for this. It can't record anymore, but was sold for being able to rewind/fastforward 3 tapes at once. Haven't become yet that nerdy about tapes. If they decay over the years... well, that's unfortunate reality of medium. I have yet to hear any tape from my own collection which sounds shit due age. It is more about some tapes getting damaged by inferior player with less-than-perfectly lined heads which have damaged tape itself. Always utmost horror.