I have a Case 1550 dozer. You need to post close up pictures of the undercarriage to verify if there is really 80 to 90% life left in them. For me, this is a huge red flag for a machine that old. It's rare that somebody spent the money for a new undercarriage, and from what I can see, it's been used for a very long time, which means the undercarriage has a lot of wear on it.
Case does not support their old equipment. The dealer may or may not have parts for it. On mine, the fan broke off and destroyed my shroud. Case does not have that fan. I had to find it at a salvage yard in Florida, where they also had the shroud off of another 1550 dozer that they where pulling parts off of. Including shipping, this cost me $2,000
Mine has a Cummins engine. You cannot buy engine parts for it from a parts store. Napa requires the serial number to find the right part. All Case serial numbers come up on the Napa computer as not being available. You can only buy parts and rebuild kits for the engine from the dealer. Fortunately, they have had those parts and the prices where similar to Napa.
Every time I've had issues with my dozer, my local dealer has gone out of their way to help me fix it myself. They copy everything needed from their manuals. They tell me where to get the best deal on parts and other places to do work on it. They just about totally refuse to work on it themselves.
When one of my hydraulic pumps went out, Case wanted $25,000 for a new pump. They didn't want to do the labor, and would not quote me a price to do the labor. They also told me about a place an hour away that rebuilds the pumps if I take it out myself and bring it there. Cost to rebuild the pump was just under $3,000 with me doing all the labor.
My dozer is 170 hp. It was big enough to dig my pond, and big enough to move a lot of dirt, but horrible at removing trees. When the ground is soft in the Spring, it pushes them over pretty good, but it also snaps them off from time to time and leaves you with a nasty stump to deal with. Most of the trees it pushes over are in the 12 inch range. Bigger trees require digging around the roots, and building up a ramp to get the blade up high enough on the tree to push it over. This is slow going and it creates a huge mess to clean up. Once the trees are on the ground, pushing them into a pile to burn adds a massive amount of dirt to the burn pile. I bought a rake, and that helped, but the trees still push dirt as they are pushed to the pile and you still get a bunch of dirt in the burn pile. A dozer is probably the worse machine out there for clearing trees. Once I realized this, I stopped using the dozer for trees and now use my backhoe for tree removal. I put a grapple on it so I can pick up the trees and carry them to the burn pile. Clean trees burn faster then trees mixed with dirt. Clearing trees with the backhoe is significantly faster and easier then with a dozer. I believe an excavator would be even faster at taking them down, but not as good for getting them to the burn pile.
I still have a few things left to do with my dozer on my land, but then I'm looking forward to selling it and never owning anything with tracks again!!!!