Years ago I went into partnership with my father-in-law on a wheat & cattle operation in Oklahoma. We had two combines, Massey-Harris 90 & 91, great old machines powered by Chrysler flatheads. Over time I became an expert on those antique machines, as I had to keep them running. The hydraulic pumps on our machines were always leaking oil--had to refill them constantly, and they needed replacement more than once. FINALLY, one day my father-in-law produced the operator's manual and shop manuals he'd had in a closet somewhere. He'd left school in the third grade (had to become man of the place when his father had a stroke), he couldn't read more than a bit, so the manuals were useless to him. They were gold to me.
First thing I learned was that you needed to check the oil level in the hydraulic pump WITH THE HEADER DOWN, which was inconvenient but necessary since the huge hyd. cylinder to raise the header held a lot of oil. We'd always been crawling in the easy way with the header up and filling the oil that way--which blew the seals on the pump.
So yes, more than likely you've blown seals by checking oil level with cylinders extended.
