Rear main seal doubts and oil leaks solutions

I am having trouble with the rear main seal of my XJ (1988 4.0 Renix). It was replaced a few months ago and it's starting to leak again, so I have some thoughts, let's see if there's something right with them.

1. It started leaking a few weeks ago in a whelling trip. Is there something that can cause the seal to start leaking after some heavy usage / abuse? I didn't really hit anything.
2. Can bad motor and tranny mounts cause early damage to the seal?
3. I bought a generic one last time, maybe that is contributing to a soon failure, but here in Mexico we don't have too much options for old vehicles, but I found that Autozone might have the following here in my city: FELPRO Rear Main Seals for a 1988 Jeep Cherokee 4WD, PN BS40612. Would this be a good guess?
4. Any other ideas assuming that the changed seal did work fine for a while?

And, I also have trouble with my valve cover; it has a new seal but it still leaks. My technician told me it was somewhat bend, so I should consider replacing the valve cover. The 1988XJ has a terrible choice of a valve cover, so I'm thinking about one from a 1992 or similar XJ (with a much better oil cap). What would you consider to get a cheap and good solution for this?

Regards

Pull the valve cover and find a nice flat steel table saw or jointer so you can lay it flat on a truly flat surface. Then take a feeler gauge, long bent type and work your way around the valve cover. Find the gaps where it's tweaked, mark em with a highlighter then gently bend them back to true. Repeat as many times as needed. Once you have a good flat surface put it back on the head, hand tighten the bolts and snug them up all the way around in a cross pattern just like a head. Final step is torque them to specs, 12ft/lbs or something like that...
Next thing is see if your 'rear seal leak' goes away, valve cover leaks do a very good impersonation of a rear seal leak..
The trick though is to do it on a truly flat table and the kitchen counter is not a good option..

If I use the kitchen counter, my wife will kill me. But I'll see if I do that, I just don't like this valve cover because the rubber oil cap leaks all the time, I would preffer a plastic oil cap witch can be screwed on and seals with a seal (like the first HO). As far as I've seen, it can be adapted easily, but I'll check the valve cover before replacing the rear main seal again.

the vavle cover does not need a gasket/seal. take it off and clean up the cover and the top of the head. then lay a good bead of silicon around it. that is all they use at the dealer and I believe it so states in the FSM. this will take up any small deformities in the cover. good luck

Make sure the small plastic line going from the valve cover to the intake manifold is open. Blow through it.
The large rubber breather from the valve cover goes above the throttle plate. The small line below the throttle plate, into the intake manifold. When you back off the gas suddenly, the crankcase pressure goes up quick, if the small line is plugged it can force oil out of many places. Valve cover, dipdtick, air filter box, main seal etc.
I had a middle serious rear main seal leak on the wifes 87, after cleaning the crankcase vents (both) the leak dried up to a seep.
Sometimes the seal wears into the crank surface and a new seal doesn't last long. FEL PRO supposedly (I've never been able to find one) has a double lip (or offset lip seal) so the sealing surface is slightly off from the original spot. Theoreticaly this should seal better and last longer.
I've had poor luck with the normal Fel Pro rear main seal, better luck with the Crown automotive and OEM seal.