This has probaby been posted previously, but...
A couple of Yamaha (US?) part numbers for oil change stuff. The drain plug crush gasket is 214-11198-01 and an o-ring that will work for the oil pipe is 93210-10096-00. The drain plug gasket was $0.99 and the o-ring was $1.50. I think by the MZ spec the o-ring is 11mm inner diameter and 2mm thick. The Yamaha part might be a tad less in diameter but it fits and works well.
BTW, if you are silly enough to not get one of those oil pipe bolts back in correctly, the Heli-Coil M6x1 kit at your friendly auto parts dealer is $30. You should hope your lucky enough to have the upper one strip as at least you can get to that one straight on. I won't be removing the bolts all the way to do an oil change anymore...argh.
kman