I have a 2006 LT2700-60D with the 27HP Generac engine, Model 0050581 and Serial 7818389. I fill with oil before mowing, and the oil level after 2.5 hours of mowing does not even register on the dipstick. No external signs of a leak. I assume it must be burning it, but no exhaust smoke or loss of power. I've been using Mobil One 10w30 for years without issue. Upped to 20w50 with no success, in fact it may be a little worse. Other than burning, I don't have a clue as to what it may be. It's always used a little oil, but not like this. Any ideas?