I have always used dino oil in the bikes. In all my years (beginning in 1990) of being a Brick owner, most all seal failures I've read about seem to be to those using synthetic. I do 5K changes on the bikes. Oil related failures are rare and spending more doesn't make me fell better.
I keep my vehicles - 100k on the first '85, 40k on the '02 LT (totaled), 85k on the '05, 150k on the '02 F150 - drive them until I can't figure out why it isn't running well...
I use synthetic in the car (06 525i) and '14 van as that is what is recommended by the factory. Longer change intervals on these and it monitored by the vehicle. The car has a 15k change interval, currently it is telling me I've 9k to go on top of the 10k it has already done.
I live far out in the country and whatever I am driving/riding is going at least 10 miles, more likely 30 miles, every time I start it so it is getting fully warmed up each cycle.