I'm pretty sure I'm one of the few, if not the only to experience this - strange issues keep appearing on my 211,000km bike. Yesterday I couldn't lock the seat.
Closer inspection show badly worn locking plate/hook and pin.
New/used locking mechanism might be available.
The pin is another story.... I thought about welding a lump on it and then grind it back to normal, but the seat pan plastic is quite close. Too close?
Thoughts?