Thinkpad T60 Dimm slot or board problem?

[Skater]

My Thinkpad T60 6371 has been working great from the day I got it over a decade ago. However, it just started locking up and posting numerous horizontal lines, several inches long on the screen.

When that started and I tried rebooting, I was getting 1 beep + 4 short beeps + 1 beep + 1 beep, which indicated to a bad slot or system board. However, the laptop would reboot if I removed and reinserted the battery.

I therefore removed the Dimms, and tried inserting each one into Slot 1, which worked fine. So I’m assuming the problem must be either Slot 2 or the system board.

My questions are:

(1) Is there some way to tell whether its the slot or the system board?
(2) Can the slot be replaced without removing the board?
(3) Most of the used T60 boards on Ebay are 42T0165's. But my board is marked 42T0166, and there are only a few of those around. Moreover, the 42T0166's, they’re much more expensive than 42T0165's. So I was wondering if I can use one of those instead?

Thanks very much in advance for any help anyone can give me, as I’d really like to keep this laptop.