Not sure if it applies to a 124 but I scavenged diaphragms from the yard for my 85SD. The double pods have 1 diaphragm that is different from the other in the same pod but I was able to make a working set with a few pods from the yard. Usually only 1 of 2 diaphragms in a double was broken. The other diaphragm interchanges with the single pod.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.