Serial number is located by one of the screw mounting holes on the underside. It should be opposite the "made in China" print. Serial number has letters and numbers in it.
The co-witness from a milled hellcat slide with the 507k isn't too bad. You can see 70-80% of the front sight. FWIW check out these reddit posts and youtube of the co-witness and see if it's something you could live with. If you don't want to mill you could change to suppressor height sights and...
I personally wouldn't waste the time trying. Give springfield a call and get that RMA for it. It's highly unlikely it was a bad battery and it's definitely a manufacturing defect. Springfield customer service informed me the somes wasps weren't dimming properly.
I would probably mill the slide for the holosun 507k at this point. I've seen youtube videos of it on the slide with no plate and it looks good. Most importantly, it works beyond 1 month and has a shake to wake function. Cowitness is good too when milled.
I'll report back after a few weeks of my replacement. So far it's been only 3 weeks. The wasp does seem to be dimming in the dark compared to my original one so that's a good sign.
The instructions say the wasp is IPX7 rated which is waterproof up to 30 mins submerged in about 1 meter of water. I probably wouldn't worry too much about it. If water damage does occur though, RMA it because it's a lifetime warranty.
You're experiencing the same problem of the wasp draining the battery in 4 weeks. You can choose to contact springfield for a RMA now or try your luck and replace your battery, only to confirm in 4 weeks what you already know, which is you have a bad wasp. Good luck!
I received a new unit. And a note that said "Replaced. Springfield is sorry for this inconvenience. Thank you for your loyalty to Springfield products."
I recently sent my wasp for battery draining fast (dies in 4 weeks) in and it arrived on 1/10 to springfield. They shipped out the replacement on 1/19 and I got it 1/20. I wrote the date installed and voltage (meter checked) on the battery. We'll see if I get longer than 4 weeks battery life on...