They are the symptoms you describe---you can only replace the caliper. There have ALWAYS been problems with Volvo Calipers---particularly the 240 Bendix. Wecome to the Club
Don'screw around with it--get a rebuilt one at Auto Zone or O'Reilly. I would not recommend a used one unless you know it is of good operating condition. Get used to servicing your Volvo brakes regularly, and usually, more often than other types of Imports---they are a thorn in 240/740 Series---if you need other parts or advice---drop me a line---I did six years of Volvo reconditioning---and have the parts supplies to prove it