Hi grumpy,once apon a time i had a mini in which uses the engine oil to lubricate the engine and gear box/diff.i also was supprised to read that the oil i used was of the correct type.the oil lubricates the diff/bearings and runs through the pump to obtain drive.it does pass through a internal filter at all times and you fill the whole hydro via the fill plug at the top so the level is 1/4 inch below the fill plug.after first fill i had the rear wheels off the ground for clearance and rotated them by hand back and forth then rotated the pump drive (where the belt goes on the pully with the fan)then started the machine for a minute and stopped.lowerd the mower on the ground and let it sit ans settle for half a day-re checked oil level and topped up,then went for a little drive forward and backwards-made a minor adjustment on the heel/toe linkage and have now used it on 5 1/4 acre blocks with excellant results.dont close this yet as i will get my daughter to do a link to the mtd hydro site and some picks...ken
