You could also drill two holes in each cover, but a grade 8 bolt in each hole, then use a long wrench or pipe or something to lever against the bolts and unscrew it. But I'd only do this as a last resort if they're really trashed. Also: be smarter than me and make sure you don't let the lever come loose and hit yourself in the forehead. I got really tired of explaining that bruise.
In less than optimal circumstances,
creativity becomes all the more important.