Luke, the starter may very well be ok. It's likely just the solenoid is fried.
There is a pictorial about rebuilding the starter somewhere on this forum.
On the subject of rebuilding, stay away from rebuilt starters from McParts.
Most of there are reconditioned with substandard Chinese and Mexican pieces. You will have problems with them. If you are comfortable changing out the starter, follow the instructions on the pictorial and use the OEM solenoid. Or take it to a re-builder, and insist on OEM parts, Or use a salvaged starter. I'd take a good used starter over a "lifetime rebuilt McParts" starter any day.
Jonj

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Jon J.
81 240D