I paid a premium for a titled '89 HMMH, but got a bargain on my '87 SEE (followed by much aggravation due to bill-of-sale-only, plus some extra fees, still a bargain if I value my time at min wage
. Totals: $55K, 30 hours rebuilt, 800 miles. Hard lesson learned: tilt the cab and re-torque the head bolts on RR depot rebuilds, two reputable old salts grinned and chuckled at my sob story. -30*F, I tried the ether-shot on the SEE last winter, not sure where it stuck but I had to bail outta the cab when I felt the buzz kicking in, only then did I see all the steam coming out the stack. 110*F later, on its next (jump) startup, all was well -- but sure gave every indication I'd blown the head gasket, sounded the part too?
The SEE was less cherry, but also better taken care of (aside from incorrect head-bolt torque afaik) -- every zerk freshly greased. I'm not an expert on military affairs, but there's a TO (not TM) in with the rest here, which covers the greasing issue.
My HMMH never hit a maintenance interval, so its zerks aren't even scratched! 85*F - -40* where I live, 3-5 pumps per zerk spring & fall will be my interval, even if they don't need it as per operating hours / miles. If you get a runner, grease 'er up good first thing! My HMMH has tell-tail stains on the flat-green paint job, where the grease all melted out. My SEE had visible fresh grease, upon arrival, but winter here means sand & salt, so pump that grease out in the spring and refill it in the fall.
First test of the suspension lockout on the HMMH cracked the reservoir, apparently a known problem which hadn't manifested pre-sale. Plus two leaky hydraulic cylinders, one major one minor, same deal -- cherry HMMH only ever been driven, without exercising various systems, stuff gonna dry rot. Those crane seals took five weeks to get, why I ordered plenty, I don't remember what I was told about the OEM on the crane, or the company which now owns that brand?
Air leaks on the HMMH, has 4x4 but no diff lock? I found some interesting info here on fixing this issue, which isn't covered in the "unit maint" manual, once again a case of stuff just sitting around not being used -- cherry FLU's, imo, really are too good to be true! Unless you take the time, upon acquisition, to do all the routine maintenance they require before ever starting the motor. Plus a few extra checks like head-bolt torque.
If only I had it to do over again, on both my "new" Mogs! Nutshell answer to OP: none of these issues presented pre-sale, nor would any have been deal-killers -- negotiating points, sure! I've had a couple of heartaches, despite not even having used either of my FLUs yet, because I didn't hit all the routine maintenance (and then some, like the air system, head-bolt torque check, drain the ether and use distilled water plus some WD-40 on that dash-mounted self-destruct-switch) before ever starting them up, after taking possession. My HMMH won't see much use in winter, but I will take her out of the barn twice a month and just warm up & work all the hydraulics, in this cold dry climate. There's nothing I could've done to keep her from spewing hydraulic fluid the first day I had her, this sort of equipment just doesn't take kindly to sitting around. Although, all hoses on both mogs are good.
My cold-weather mods so far: hydronic heaters & heated dipsticks, full fuel-line replacement with standard rubber fuel hose -- the 30yo plastic hoses are so brittle they aren't likely to last long around here, so Preventive Maintenance. I have lots of real-world work to do with mine (the SEE's getting a universal skid-steer adapter & belly PTO to run a snowblower) before they're relegated to garage-queen status, but even then, they need to come out & play. Day/night difference in my two mogs, one sat around, another was cared for 2x for every hour it was used -- even came with two spare oil filters, one spare hood gasket, full printed manuals, and a Unimog ballcap!