Can the Seadoo OEM synthetic blend be mixed with standard off the shelf Castrol 10W-40? The Castrol oil meets all of the specifications that the owners manual and service manual list out but is way cheaper. If I use the oem in one engine and later switch to the Castrol, will there be a problem with mixing oils? Especially since when an oil change is done, you can't remove all of the oil from the engine.