Hello everyone. I have a Delta Monitor shower faucet which through searching here I've found is a model 1500. I'm going to post a pic to be sure. It drips slowly and I'm getting ready to sell the house and do not want a leaking faucet. What I need help with is disassembling it to rebuild/replace whatever is necessary to fix it. I removed the handle, the temp. control knob and an 11/16" nut that went onto the white part around the stem. This is where I'm stuck. The chrome assembly there will not move. Am I missing something? Or does it take extreme effort to pull off in order to reveal the parts I need to change. Thanks to anyone that can help. I truly appreciate it.

This is the fixture:

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And this is where I've run into problems:

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Thank you for your time.