Looks to me this battery is 16 years old.  Impressive.  But perhaps not appropriate to offer at any price...maybe is use it for my model plane battery charging...

I have yet to replace the exhaust gaskets on any of the four bricks I've owned and had no issues.  Once I learned to close the throttle when coasting almost all the backfarting stopped.

As far as the "copper" nuts, they're just copper plated.  How much of that copper plating do you see on the nuts that are there now???  I save lots of my money and use stainless nuts and studs from McMaster Carr

This was a helpful post. My k75 side stand gives me worries.  The hockey puck under the foot idea is interesting, but not if it masks a member in the side stand or joint. That are wearing to a point of failure.

My thought on the puck is a plate with a catch for the foot that will slide out and in but not slip off the plate once captured.  So, a horseshoe shaped keeper on a 4” square piece of metal plate.  Someone has made one of these no doubt.  Cheers.

Reduced.

Yes, usually air entering exhaust will cause popping,... but these bikes do that anyway. If it is not leaking visibly, I wouldn't worry.