van has misfire on cylinder 8 and has low compression.

What is your question?

The van(85,000 miles) was in storage for about 7 months and when I went to go start it up it started but was driving sluggish. The next day when I started it up and just as I turned the key over there was this loud clank,clank,clank noise(like metal was hitting) for about 2 seconds and then the van started running really rough and the service light came on. I took it in and they said there is a misfire in cylinder 8 and they changed the spark plug the coil and it still was misfiring. So they did a compresion test on that cylinder and said it has low compresion like 30 psi. They said it needs the cylinder head to come off because there is damage somewhere there. Anybody have any ideas as to what could of happened, someone told me that maybe the valve was stuck open and the piston hit it, or the rocker arm came off or the valve spring. Does any of this sound right? I would appreciate any help or suggestion. Thanks, tkj