For on-site service, I don't think $500 is bad. It's not just the distance traveled and the time involved, it is having all the tools and supplies stocked in a truck to do all the work out in the field.
I work part-time for a truck and trailer shop. We do all work in the shop, but there is one...
I agree with finding a local shop. I have a local guy and know that he's using quality parts for a rebuild. Getting a Bobcat new part would be equally good, but expensive. At least for automotive alternators, I've found the typical parts store rebuilt alternator isn't the greatest.
The design of the drive chains is meant to keep the front and rear wheels on one side at the same speed. You are going to add stress running them at different speeds due to the tire chains. In snow or on dirt, this may be negligible. However, as foton says, hard surfaces or loading could...
I'd say the very first thing I look at is weld quality. It really speaks to whether the manufacturer cares at all about what they're putting together. Bird poop, booger, or bubble gum welds mean I don't have to look any further.
Unfortunately, it is sort of the nature of the beast with a small enclosed space like that. Moisture inside the space condenses on the cold glass - anything from ambient moisture to your own breath adds to it.
Air circulation helps. You could add a small fan to circulate the air, but this would...
That does look like an oddity. It has the rear posts and cab similar to the B-series, but has the side panels and arm configuration like a 610.
Here's a 520 and 610. Yours seems to be between the two of them?
As Wayne says, it is likely better than by doing it by hand. Capacity on it is about a quarter ton, so there will be limits to it. My Bobcat 630 is about double that. I find it very useful, but have run up against that capacity limit at times.
I'm not sure where you're located, but as Jyuma mentions about hydraulic fluid being thinner combined with cold weather the 15w40 could be pretty thick. Add in old components and you're putting extra strain on things with that thickness.
You can go over specs of current machines on Bobcat's website: https://www.bobcat.com/na/en/equipment/loaders
The simple answer is the higher number machine will have higher horsepower and rated operating capacity. Other differences may be radial lift path versus vertical lift path, high flow...
Another safety issue - resist the urge to climb in and out of the cab under the arms when they are up. Every few years I see a news article about someone being crushed when the arms come down for one reason or another.
Messick's is local to me: https://www.messicks.com/
But I've seen people from all over the USA recommending them on other forums as one of the "go to" places for parts. They seem to be doing things right.
As others have noted, the damage was likely done before you purchased it. The leaks were basically there, just clogged up by the contaminated fluid. The fresh fluid got things flowing - both properly and through the leaks. The contaminated fluid is also likely to damage pumps and motors and...