Clearing snow is harder on a blade than one might think. Some good answers here on sudden shock loading due to manholes, frozen soil, curbs, pipes, and anything else that is hidden under snow. The constant vibration feeds back into the cold metal of the blade frame and linkages and weakens them over a period of time. The moldboard takes a real beating and if plow bolts are not kept tight, the bolt holes elongate and after that, the bolts can not be kept tight. Same with the moldboard brackets and slide bearings. If they come loose and are not taken care of right away, they will never be tight again without some rebuilding.
The final drives and chains take a beating from the near constant slipping and traction conditions encountered with snow plowing. Especially if the blade has been run with traction chains, as most are in winter. The chains become elongated and can cause jerking and sloppy brake engagement. The hoist cylinders take a beating as does the lift and side shift frames, again on cold metal. Look for cracks at all major welds on everything connected to the moldboard. Check for damaged brake lines at the final drives, chains tend to beat them up pretty bad. Generally, the swing gearbox gears, either brass or aluminum, will show more wear and tear than a blade just used in dirt.
About the only thing worse on a blade is working on haul road maintenance in a hard rock mine. But 140's or 143's are not often used for that purpose.
Oh yes, if the blade has been equipped with a wing plow or a vee-plow, look for damage at the frame where the wing was mounted, and check the front axle mounts carefully. That vee-plow ads a lot of weight to the front. Constant cold weather operation can damage the hydraulic system with excessive moisture and shock loading to various components. Cat's accumulator system helps with this, if it's working properly. Moisture is another matter. Besides causing extra wear on bearings and seals, it freezes and can cause cavitation and other problems.
These blades work in a harsh environment of brine and salt, which causes havoc with electrical wiring and switches. If they are not washed often, the corrosive effects can cause shorts and opens that are difficult and expensive to find and repair or replace.
There are a lot of good reasons state and county road departments get rid of these machines at 6-8000 hours. They still look pretty good and still usually run decently. But they are on the top of the curve at that age and start to lose value afterwards. Time to trade for new fairly trouble free units from a cost standpoint.
Be very careful with your purchase and make sure someone competent looks at the machine first. Check the units previous maintenance records, get a sims report from your Cat dealer, and try to get all the oil sample results from the previous owners. Good Luck!
