Mine are still working at 40 plus years just fine. 3BST's still have about 20 years to go before they can hang with that, and by then mine will be happily making music at 60. Perhaps Yamaha didn't offer a 20 year warranty because it wasn't necessary?
Let's see how many parts can be replaced on a 3BST in 20 years. We lose more and more through hole components every day. You can always put some semiconductors away now, but the right electrolytic caps to keep it running may be just as unobtanium as a V-Fet.
Anyhow I'm out of this childish conversation that is an unfortunate distraction from an otherwise very good and informative thread.