My very old Exmark Viking has one pump that has started a leak at the bypass valve lever. This pump has 1,000s of hours, perhaps 8, and has been solid. The counterpart pump on the other side was replaced in 2008. I did not have a leak when finishing the 2013 season. But, I had the mower out a few times over Winter, running to warm up, a few passes around the drive. I had opened the bypass valve so that I could push/pull it into a Winter parking spot in the garage. A couple of weeks ago, I had it out running, doing some maintenance work. I noticed a drip under the valve, the oil on the engine deck. Today, I took it out for the 2014 season for the first time. I finished one job, went to the next, and noticed a considerable amount of oil on the deck. I watched closely and a drip was happening about a 30 second interval. This means it is substantial, and will loose considerable amount of oil over a day's work. I am in a quandry. The machine is 18 years old, engine still in pretty good shape (uses a little oil, but runs well -- a 15 hp Kohler, single cylinder). The other pump was replaced in 2008, but neither wheel motor has been touched. I always consider the pumps and wheel motors as the most vulnerable for failure. I believe the original pump is a Hydro Gear BDP-10A. The replacement on the other side was a BPD-10L-117 (according to my purchase record). The Exmark part number is 1-613042. I find replacement pumps online as BDP-10L-117P, at a wide range of prices ($450-$700). I have never rebuilt a pump, and am not confident enough in my mechanic skills to do so. I don't know what kind of seal might be involved with the bypass valve -- maybe this repair is relatively easy, without having to tear apart the rest of the pump. It is interesting there was no leak at the end of last season, but showed up after the machine sat idle over the Winter months (excepting having it out to run for awhile several times over the Winter). I never open/close the bypass valves during the runnning season, but use them every time to park the machine during the Winter. Apparently, exercising the valve a few times over the Winter was enough to create the leak, a leak from a weak seal. Thoughts? Try to repair? Replace with a 10L-117P? The expense of a new pump on a machine this old is questionable, but spending $5,000 for a new mower is also questionable. I expect to use this machine about 300 hours per season (used it many years as the only machine, but moved to part-time after buying a ZTR five years ago).