Wow, I just got a TDS5104 and all the encoders barely function! Took the unit apart, and found these are semi-custom jobs that are integrated right on to the PCB! So much for replacing those!!
I was able to fairly cleanly remove the dust caps (which also control the detent count, so don't mix them up) and clean the insides with alcohol and cotton swabs. (making sure I didn't leave any fibers behind). They now work pretty well, but what a major hassle to melt the heat stakes, clean, re-assemble, and reform the heat stakes
I wish they used standard off the shelf rotary encoders. I would have replaced them all by now much easier, and again in 10 year.