Unless you are completely without a basic tool set and an hour or two, I would encourage you to at least try the repair yourself... it's really quite easy. Call CASCO Thunderbirds in PA, or similar, and they'll ask one or two questions to confirm vintage (early or late), and send you a complete kit (more stuff than you need) for $35 or less.
Drain reserviour with turkey baster, remove feed and return lines, three bolts will loosen the mount for belt slack and removal from motor. One bolt removes lid and filter, and two or three (depending on style) will remove the resv from the pump. Lastly, five more bolts will unfasten the two halfs of the pump. You may have to use a thin blade or similar to separate the halves at the seam, working around the circumference of the pump.
By this time you should have found 2 small and 1 medium o-ring between the resv and pump, and 2 small (plus maybe 1 medium) and 1 large o-ring between the pump halves... simply wash/rinse everything with clean ATF (FA Type), replace all the o-rings as you reassemble, torquing bolts 18-20 lbs.
Put it back on the motor, plumb, tension belt, fill, and start the motor. Turn the wheel stop-to-stop a couple times, and check for leaks. DONE.
Worse case, you out $35 and some time, but you gain knoweldge and confidence in return. When you have the halves apart, you should inspect the impellers for chips, burrs or heavy scoring, but if you had a problem with these, you would have already noticed it noise from from cavitation or piss-poor response to steering input.
Go on... go for it. If you get stuck, someone will be here for ya.
Brian