Quick question - my '87 4Runner SR5 alternator is dead (likely thanks to the power steering pump leaking fluid right into the alternator) . So I need to either rebuild it or replace. Can you tell from these photos if it's OEM Denso or aftermarket?

I'd rebuild it if I thought it was original Denso, but I suspect it's not, but rather an aftermarket unit. In that case I'd just get another.

 

I took the cover off and saw markings, as well as a sheetmetal screw in the brush holder mounting hole that was obviously stripped. So at best it's been rebuilt. I'll probably spring for a remanufactured Denso unit.

 

That looks like an OEM alternator to me, although it has been "repaired".

 

Yup, agreed. I don't want to rebuild a rebuild, so I just ordered a remanufactured Denso 27060-35061-84.