you also could have a broken c-clip which has jammed the piston in some way. Take a look at the servo posting I did a while back (mid Feb) The c-clip is a common failure I learned and there's an aftermarket rebuild kit. I too doubt that the servo cover would fail... the bigger thing is, if the bolts have been pushed out, you're likely faced with tapping the hole larger as I'd doubt the threads will hold. this job likely could be done with the trans in place but would be tight.