[Britwrench]

Letsgojets..

Your shop is right the chain doesn't normally break..what happens is the tensioner chain guides break and jam the chain, which stops the cams (but not the crank) takes the teeth of the cams, bends all the valves, sometimes breaks the mounting boss of the cylinder head and basically makes a mess. This is very common and you can find a plentiful supply of broken 944S for sale. I would have a look at the tensioner blades at the next service.
If you change the oil regularly and don't do a lot of slow driving (in town) and live in temperate climate this problem seems to be less common. BUT it happens..a lot