Delta Monitor shower faucet??

I have a Delta Monitor shower faucet that is dripping badly. I have read there are 1300/1500/1700 series Monitor faucets. How can I tell which Monitor I have????
I was going to replace the cartridge assembly and rubber seats/springs, etc.. Worst case, cut water off, remove cartridge and take to plumbing supply store for a replacement. Actually may try just replacing the rubber seats first.
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