I haven't been doing much bike work lately, nor even much riding or visiting BF. I've been out a few times this summer and we have taken the tandem out a few times. Been having trouble with the tandem's drive train. Time to do some investigation.
Do you see anything wrong here?
Time for new rings and chain (not installed yet). Ignore the dirty bits. I guess 15,000 miles will have an effect.
New tires too.