I have a new to me (1989) mfr buckmark that I'm having issues with. Cleaned, and lubed per factory recommendations. It will fire, eject spent case and load a fresh round, but won't cock the hammer. I have tried about 10 different types of ammo, high velocity, standard, etc. I replaced the recoil spring, and buffer also. Any help would be appreciated. Thanks.

Sounds like you have something in the sear or hammer that is either broken or gone weak. I'd call Browning and ask about their warranty.

I've had same thing happen to my buckmark.  Turned out to be a build up of carbon.  Started to take the slide off for a complete cleaning and a chunk of black plastic fell out.  After puzzling over it for a while it dawned on me that it was not a chunk of plastic, but carbon.  Don't know where that first piece came from, but I popped out another good sized piece from the firing pin channel.  Cleaned it up, put it back together, and it ran like new.