On the undercarriage, I'd think, if the pins/bushings were turned, to the unworn side, with a decent amount of the rails left, that would get you some adjustment back and quite a few hours. If the rails are so worn the pin bosses are hitting the bottom rollers, then its either P/B turn, new chain, and existing pads at minimum. Pads at 50% would not bother me, as it would seemingly match the rest of U/C wear anyway, for general use, it should not matter, unless for some reason you needed full grouser height to reduce slippage.
10K would seem to be a little high, and many here suggest that without the 4 in one bucket, (does it have one ?) it lowers the value. I've ran a lot of 955's and 977's, most without a 4 in one bucket, would not bother me, but they are handy for picking things at times. I have seen a few 955's over time listed locally, usually below 10K, again things will vary geographically.
New undercarriage, what are the specifics? all new oem Cat components, sealed and lubricated (S.A.L.T.) Berco or what have you.
I would think that if you were to replace an undercarriage, and I assume that is available for 7K, you should get a few thousand hours, obviously adjusting tension, soil conditions, operator habits, and general maintenance, like turning pins and bushings when and if the time comes, all contribute to U/C wear.
These models were known to be reliable, every one I ran was, and they were old then, but I've done everything from loading trucks, clearing/grubbing, handling pipe with forks on the bucket and a myriad of other things. I even just about stood a 977L on its nose when some void under the ground collapsed when I had a full bucket over the sideboard of tandem dump. You could stand under the drawbar.
I don't know what is prone for problems on these, you can check the final drive compartments for metal fines or pieces with a magnet dipped into the oil, use a bar to check the sprocket for any free play, both could signal problems, can't claim to know much about the powershift in these, what to know or how to determine condition besides running it until its at operating temperature. Pins and bushings on the loader, tight or noticeable wear.
These don't usually have wide track pads, nor do they have oscillating track frames, so they won't contour to uneven terrain, they are big and heavy, need firm ground to work on, as long as they don't sink in, usually ok with some mud etc. but don't take one into soft material around a pond or marsh, where you need an LGP dozer, excavator or it just needs to dry our etc., as you may regret getting one of these stuck, they are heavy.
Given their popularity has dwindled, replaced by excavators, they may be obtained reasonably and are a respectable choice for what you want to do, its not a bad decision to own one, as long as you know it checks out to be field ready or can be without high additional cost.
I'd offer less, say minus the value of pin an bushing turn at least. Here's a case where undercarriage replacement, exceeds the overall value of the tractor. On the other side of it, undercarriage repaired, its field ready, you know what you have and the hours to expect out of it.
Photos would help here.
