How to repair 400 keyboard?

I picked up a 400 the other day. It is working great except for 1 column of 4 keys on the membrane keyboard (X, S, W, 2, if I recall correctly).

I haven't had a chance to crack it open & inspect it yet, but is this a common problem that's been documented & easy to fix? I'm hoping that it's a cracked solder trace or loose/bad connector that a little wiggling or solder reflow will fix.

Thanks,
-Jason

PS--I'm going to sell it. If anybody wants it as-is or after a fix, let me know. It has its power supply, RF cable & switchbox, & a handful of controllers.