I'm with John C on the foam pigs. A kit of those and the driver can't be all that much. That would be a good way to inspect the internal condition of the lines and give them a scrub. Watch for filtration carts on Ebay and auctions. I could have purchase one last year for $600 but I did not need 2. That was a bargain for a Parker unit. A guy at one of the better hydraulic shops that I've dealt with told me that diesel fuel is considered a good flushing oil. I keep a barrel of that that has been mixed with oil from previous flushes for flushing other systems with my filtration cart. It gets filtered down to 2 microns before entering a contaminated system and allowed to run for several hours. Be sure to run every hose, valve set and fitting if you don't tear everything down. It's much cheaper to spend time on the labor that another pump or motor. Most importantly, find a good, quality hydraulic shop that is meticulous. I made the mistake of dealing with a wrong one that does not care. The pump I got back had black crap in it when I inspected it so I had to tear it down and clean it before I put it into service. They had disc grinders running in their hydraulic rebuild area - that should have made me walk away and find another shop right then. Lesson learned. Hydraulics should be treated like OR's and chip manufacturing facilities where cleanliness is the standard, not like a junkyard rebuild service.