what's the reason you're interested in the switch?
There are differences in oil, mainly price.Never really thought about which oil to use. I would just use whatever the owner's manual says to use. I can't see there being a problem with following the owner's manual.
Check out posts #5 and #16: http://gl1800riders.com/forums/showthread.php?282345-10-40-or-10-30-weight-oilThe owners manual on the 1500 valks and the 1800 wings recommended 10w40 where as the new wings and the 1800 valk states it needs 10w30. This is the same engine, so they must have found an issue with the heaver oil.
My Dealer put put 10W-40 in mine for the 4K service. FWIWThe owners manual on the 1500 valks and the 1800 wings recommended 10w40 where as the new wings and the 1800 valk states it needs 10w30. This is the same engine, so they must have found an issue with the heaver oil.