So, I've been messing about with both the Delta monitor faucets in my upstairs bathrooms, both have been leaking for far too long. Ordered the cartridges, one was nice and easy, bonnet nut came off by hand.

The second one... Oi. First off, the set nut on the handle was stripped, and after trying everything over the course of a few weeks I just decided to rock the handle till it popped off, the valve is anchored to the wood inside the wall. All good, handle finally came off. Go to twist off the bonnet nut, and I hear what sounds like a screw hit the tub - except it's a piece of solder.

I notice that there are three seperate spots where the bonnet nut appears to be soldered on.... In what situation would someone do this? What's my next step?

Thanks in advance!

I doubt it is soldered on. Soldering the nut would have destroyed the plastic cartridge. The loose solder was probably a remnant hanging on to the nut or body.

Chemical Bonding, looks like solder. Soaps and cleaners produce chemical bonding. Chemicals in the water will also do that.

Best Wishes