Engine hasn't been touched. I'm aware of the problem with air in the system. That's not it.

Not sure about injector tips. The PO said the vehicle was a running driving car when it was rear ended.

Haven't checked the compression. I bought a tester off ebay, and the POS broke the first time I used it. Fortunately the seller immediately refunded my money, but I still don't have a decent diesel compression tester.