1991 940 turbo 225k

for about three years i have been using the passenger door to get in the car and unlock the driver's side, because the key will not turn the cylinder. i'm not really the door locking type, but it is occasionally necessary and always annoying. everything works (i lock it by closing the front door and opening the back, pushing down on the knob on the front door), but getting a new key from volvo did not solve the problem (so they didn't charge me, how kind). the key works fine on the hatch and passenger side, but no dice on the driver's side. how hard is it to get a keyed alike lock cylinder, and what do they run? is there any way to fix the existing cylinder? i'd probably be willing to get a third key for the d-side only (i hate the 2-key system enough already, why not 3?). i've got to go into the door to put a speaker in anyway, and i'd like to fix this while i'm in there. any suggestions? thanks and happy new year!
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'75 164e(?), '87 240gl(350K), '84 240 gl(233K), '91 940se(225k+?)