Another 1949'er here, lol. I just recently picked up a OneMotor friction drive for my bike because certain ascents were making my knee hurt so bad I'd be off the bike for a few days after. The drive is a few seconds to put on or off the bike, so I leave it off for rides where I know I'm not going to be doing a climb. And I turn it on and just use it when I need it on rides that would otherwise really hurt. I don't want to stop taking those rides, they're the most beautiful views. Still 90% manually riding, and sold my car 6 months ago, so using the bike(s) for everything. I am taking collagen peptides and Costco's Triple Action Biocell Collagen for my knee and other joints; seems to be helping a lot. And it can't hurt, anyway. I ride 10-20 miles a day typically, between errands and exercise.