Also, now i'm thinkin straight & read the heading again--if it sucked a base gasket then that'd take the tension off the head bolts--long sleeve nut things they are that holds head & cylinder on together.

Yes, it’s an L-shaped top ring. The right rear stud area of the base gasket bulged out. That was the sign that caused me to take it apart. Would using a thin coat of yamabond on both sides of the base gasket be a contributing factor? That’s how I installed most of my gaskets. 

I just grease my gaskets including head gaskets with no trouble so far. Although my 490 sucked a base gasket years ago so i got some thicker gasket material & cut one slightly bigger on the outer edge using the theory that it would bite in & the uncompressed overlap would stop it being sucked in again. It worked whether because of that or not i dunno but never did it again.

Thanks RT.   Hope to have it back soon to put together.