I've Alway liked the cascade bracket. Should be pretty easy to make one that fits a license plate
http://www.cascadeinnovations.net/store/store_View.cfm?STORE_AREA_ID=3&store_dept_id=36
I wouldn't run it. Sounds like a head gasket but it shouldn't be oil unless there's another problem maybe coolant. Any smoke while it's running or coolant loss?
Do you have a picture of the leak? Leaking base gasket? There are no screws on a yfz cylinder just 4 head bolts and 2 studs. Don't put any sealer on it just put a new gasket. The only things that take sealer are the case halves