There is no brief reply to that one!

Rectifier - H-D unit for over 39,000 miles. Still facing front
3 sprockets - Most under warranty. Then ordered the Super Max. Killed that one in 16,000 miles. Now the new Morgan Steel sprocket. Just as quiet as the Super Max.
drive belt - a just-in-case thing under warranty. The first worn sprocket bothered the dealer so he had that replaced. The belt is not the issue. It should last over 100,000 miles!
cam belt - New spacer washers and removing gasket has done its job! Have checked every 10,000 miles and there are no blisters presaging the break point. Looks good!
old style compensator - new Centa unit two years ago. Rubber inserts replaced last year during rebuild. Couldn't hurt!
chassis - new one last year - had the brace and all. Not enough for the starting torque just overwhelmed it!
battery - stock one died - there are better
Right header due to both bobbins dying and exhaust dragging on ground bending far too much. Hot header crumpled like tissue
Left and right exhaust pipes - Left had cracked completely around at front bobbin. Internal baffle held it in place. Right exhaust showed signs of cracking. Both replaced.
Spline on S&S crankshaft showed signs of twisting. Crank and pistons replaced. A basic rebuild at that point.
Fuel pump - avoid ethanol fuels! As an aside, any contaminate that gets into the fuel tank and settles to the bottom will get sucked into the pump immediately! The intake sits on the bottom.
Right headlight due to killing deer. It went under. Had it gone over I doubt I would be here typing this...
Left tail light due to landlady's inept parking.
Brake light switch due to corrosion I think

So far, as of today, that is all!

What's your mileage? Who cares. Is it practical? See #1. What happens when it rains? You get wet.