Any way to make this tarp useable?

If you know what type of coating that would help a bit.

I would try letting it soak in paint thinner for a while and then rinse it off and see if the coating comes off.

Then you could apply a new coat of silicone and mineral spirits afterwards.

I would be worried that the nylon might have degraded over time. I'm not sure I'd take such a tarp out in rough weather.

Had the same problem with the tarp from a large Eureka family tent. Eureka said to launder it a few times in powdered (i.e. strong) detergent and most of the coating would come off, then recoat it with Aquaseal or similar.

I was able to get the coating off as they suggested. Now that the warm weather is almost upon us I plan to recoat it. Note these instructions are for polyurethane coatings, not for Silicon-coated fabrics. I don't think the latter become sticky with age.

Since I use old tents for car camping I usually bring a cheap blue tarp to throw on top of the tent if there are any leaks.