Help identifying obscure Delta Monitor valve

[CountryBoy19]

I have this Delta Monitor shower faucet, believed to be original to the house (started in 1993, completed in 1994). I can't find any videos detailing cartridge removal nor can I identify the model to ensure I get the right parts. I believe this is possibly a 17T or older variant of the 17T. The reason I suspect this is that it appears to have a brass cartridge, but I'm not positive because I can't even get it torn down to the cartridge.

Behind the temperature control knob is this white cap thing. I can't get the cap off and I'm afraid to break it. The handle won't come off with the white cap on there. Behind the white cap is a small brass hex nut. The only cartridges I can find with this brass hex nut are those for the "17T" series on some cartridge comparison sheets I've found. Does anybody know the model number or series that will lead me to help and/or parts? Does that white cap slide onto a small splined shaft? Just wiggle it with pliers? Gently prying wasn't going anywhere.

 

[Marlinman]

You have Delta's 1500 series which was the first generation of the Monitor. Bottom left shows a conversion from the 1500 to 1700 valve. Bottom right shows the pieces making up your existing handle.