I'm assuming you've played around with switching the relays and perhaps tried jumping the sockets as shown in the diagram in one of the posts. If so and the fans operate as you describe, then I'd would replace the ballast resistors on both sides to get low speed operation. The low speed operation helps the AC condensers work more efficiently.
You can replace the ballast resistors in two ways. One is the simple approach where you remove the fender liner, cut the wires leading to each resistor and splice in the wires from the new resistors. I did this and it took about 45 minutes per side. I used heat shrink over the splices to seal the connections. ILook at this thread for more detail:
http://986forum.com/forums/general-discussions/38026-c-fan-speeds.html
The other way is to remove the fender liner and the cover for the fan. Then you replace the resistors. I did not do this because of the extra work so I'm not sure how the resistor wires connect. They may just plug in.
I don't know why one fan would work at high speed and the other one would work intermittently. Perhaps the high speed fan relay is loose or there is a poor connection. No idea really.
PS: I'm not sure, but I don't think the motors include resistor packs.