Never seen it done at the factory Bob, but imagining somebody doing that day in day out explains why the cut outs are Heath Robinson.
It begs for a leather punch of the right diameter but doing that before fitting could easily miss the spot, and when fitted, access is rubbish. There's a degree of stretch in the seal and so it's important not to stretch when fitting.
"Next Time" I'll research the glue, and fit the bottom flat section on day 1. Doing the sides on day 2. This appears to be a simple job until the seal arrives flat and a few inches too long.
