Thanks guys.
I didn't think of the key contact strips as a possible culprit..and maybe that is the problem. Other Yamaha boards I have had required strip changes every year...but the symptoms were a bit different. Worn key strips usually result in specific notes losing touch sensitivity. This bass note hang up is all new to me.

I had a 4 hour job tonight and the problem did not re-occur...but I am not fool-hardy enough to believe it fixed itself.

I will check on the key strip though. Thanks again.
Eddie