This is a gm crate engine bought from a gm dealership,If you mean M as in Mexico yes it is.I have my suspicions it sat for a long time before we bought it as he gave us 500.00 off.I used quaker state 10w30 and gm oil supplement as per instructions with engine.When i got it i used an priming tool on a drill ,pulled valve covers and and and pumped oil till it came out all rockers and turned engine over with a wrench,as i was priming it.It took us awhile to gather parts before installation,so immediatly before starting we primed it again.When we started it in the vehicle we kept it at 1500 to 2000 rpm for the first 20 mins.We then drove it with varying throttle not exceeding 4000 rpm.