Sorry cfinn, I cannot guess at the cause for your parking brake symptoms. Though I've done multiple shoe replacements among ten 240s '79 to '93, I've never purchased a new cable, having pulled them from cars before sending them to the crusher.

Fact is, my only experience with a brake slipping despite having the correct force applied by the friction surface to the rotor was caused by a rotor that had not been cleaned of its rust preventive coating, but that was not a Volvo, nor my job, and a memory older than your car. But I discount that thought because you're familiar with oil contamination of the shoes.

Puzzling is the attitude of your second professional. There may be good reasons for the reticence to seek out parts not available through GCP or Volvo's network, given this to be a frequent requirement keeping 40+ year old cars of any make on the road, safety items or not. Could be they're just not in that business.

Just the same, it sounds like you do need a mechanic.

You're using this forum to reply to all in the best way it can be done here; a reply to your original post. I know the dilemma between brief enough to be read, and detailed enough to be useful. You did well.
--
Art Benstein near Baltimore

"If only Sweden awarded a Nobel Prize for recycling its cars." - General Colin L. Powell