@Lineman North Florida I'm a little late to the party, but I'll address some of your questions that didn't get answered. I've been researching this topic for a number of months and am currently looking to buy a skid steer myself. The following is what I have pieced together by reading a lot and watching tons of youtube videos on the subject and this info is specific to smaller machines (e.g., skid steers and mini ex's) as larger ones have much longer lives.
What to look for (short version):
Blow-by - while the engine is running take the oil cap off and turn it over and set it on it's opening. It should not get blown off or around, if it does you have worn rings. Another test for this is to pull the dipstick and put a finger over the hole. You're feeling for pressure.
Leaks - hydraulic, oil, whatever, you shouldn't find any, bring a flashlight and crawl all over the machine. Lift the cab and do more looking.
Undercarriage - on a tracked machine, use the bucket (or a jack) to lift the machine off the ground as much as possible. Grab the roller wheels, they should spin easy, but not wobble.
Cold start the engine - it should smoke 10-15 seconds at most and then stop.
Check the hydraulics by using the bucket and arms to lift the machine, check the arms and bucket independently. As with a tractor, the arms and bucket should move smoothly. No jerky movements.
How many hours are too many:
You might as well ask, which oil is best. This answer is also somewhat brand, or at least engine maker, dependent. I have three friends that work on heavy machinery for a living, but they didn't agree on how many hours are too many. 4000 hours seems to be the area where most people agree a skid steer is starting to get old. That being said, Takeuchi has a reputation for better longevity, as do machines with Yanmar engines or the venerable Cummins 4b(t).
My goal, here, is to buy a machine with 1500-2500 hours and as new as possible. There are machines that are 25 years old with 1000 hours, which is great, but seals/o-rigs will be drying up at this point.
Also of concern is parts availability when you get older machines. I've asked around, here, and elsewhere about when do parts become hard to find and there's no real clear answer. A common theme is some brands, for example, bobcat, support their older machines better.
Tracks or tires:
Tires for use on pavement, demo work, or on rocks.
Tracked anywhere you need added traction (e.g., mud) or where you want less impact on the ground, such as on grass. Though tracks will tear up any surface if you're doing tight turns. Tracks for snow is hotly debated and appears to depend on the machine's suspension design and track pattern. ASV states that their suspension and track design adds greatly to traction during snow use.
As others mentioned, tracks add stability and cost.
Brands:
Each brand has had good units and bad units. The new DPF and DEF and other emissions requirements seem to be causing a lot of grief. I plan to avoid as many emissions as I can. As with tractors, having a good dealer w/ parts close is important. For example, while ASV is a good brand, the closest dealer to me is 3 hours away. Some brands, for example, Gehl have a large regional presence, but it's sparse in other areas.
I'll be buying 10-20 years old, so I plan to stick with Bobcat, John Deere, Cat, Case or Takeuchi.
High Flow:
If you can get high flow, do it. Most brush hogs I've looked at have a minimum flow rate of 16 gpm. There are a lot of machines at this flow rate, but a number of older machines dip to the 13-15 gpm area. While 16 gpm will run the brush hogs, but there will be a lot of waiting for the brush hog to spin up to speed if you're mowing thicker stuff, and a lot of other attachments, more is better. If you want to run a mulcher, definitely get high flow.
Yes, this is the short version. Hope it helps.
Oh, one last thing. Some older skid steers control the bucket and arms w/ foot controls, while others (and newer machines) use joystick controls. Totally user preference as to which is better, but try both, it may push you one direction or another.
