Hi @goingnorth123,
We're on the same Oosterdam cruise as you are on Nov. 14. I have organized a private tour in General San Martin and spent a lot of time going back and forth with the tour operator to make sure I have everything right! Someone else has mentioned on this thread that the cruise lines don't let you know about the free shuttles in various ports until the last minute and I have read multiple posts about that very thing. Cruise Lines are selling "Shuttles" into the city on their Shore Excursion pages, sometimes for $40 pp and then when you get to the port, you find out you could get into the city on their free shuttles.
The tour operator in Paracas, which is 20 km from the Port of General San Martin, told me the free shuttle into Paracas runs every time a cruise ship is in port. Paracas is small town and we will be dropped off a block from the Paracas Explorer's office!
If you are on the Roll Call for our cruise, the information is on the Spreadsheet for private shore excursions if you are interested.