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This looks like a 3 handle tub/shower valve. If the diverter is stuck you'll have to replace the diverter cartridge. Here's a parts blow up to show you what's involved and the part you needhttp://www.moen.com/shared/docs/exploded-parts-views/82403pt.pdf
No, after market versions are inferior. You'll have better luck getting it out with a cartridge puller. I believe they have them at Home Depot & Lowes among others. Best to not try to get it out until you have the replacement in hand.