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https://www.simplicitymfg.com/us/en/support/results/Tractors/Regent/1693915
What year is tractor and is it still under warranty? If not under warranty, remove deck and replace drive belt, it's probably worn out. Be sure to replace with original Simplicity part number belt. Your owners operator manual might have belt part number. Now would be a good time to lube tractor, all grease fittings, as well as steering sector and pinion gears. Since your deck will be removed you can clean deck topside and underside, inspect belt for replacement and all hardware for being tight. I would also remove blades, clean, inspect for wear, and if they look ok dress them up with a file and balance blades, this should be in your manual. Lube spindle grease fittings top of deck and use an oil squirt gun to lube all moving parts being careful not to get oil on belts, if you do wipe them off.