The throwoff could be bent, which would require replacing that whole end of the snare assembly. But the more likely problem is that the lever's out of alignment simply because the plastic handle is loose and/or crumbling. It's really not a huge deal since you can scrounge up a replacement handle pretty easily. I could probably even dig one up to send to you.
BUT... Knowing how that old
Yamaha strainer design works, you can be pretty certain the vertical snare adjustments on both sides of the drum are bent. That
will affect how the guts lay on the head, but usually not bad enough to make tuning a headache. The strainer design found on
Yamaha's current drums, introduced in the mid/late '90s, is more durable.