The attached image shows my PET’s very grubby chiclet keys after cleaning in situ (ie, without removing the keypads). I used nothing more than a damp (not wet) cloth using warm water with a drop of washing up liquid added. It was a fiddly and time consuming task but there was no risk of breaking the plungers. The yellowing is the result of age and exposure to light. They could be whitened using the retr0bright process but this would again require keypad removal and I also don’t want to run the risk of lifting the print.
With regard to de-soldering ICs, am I right in recalling that BrackenFix has bought a de-soldering station and some leaded solder? If so I’d suggest some soldering and de-soldering practice on a scrap PCB would be very worthwhile as mentioned earlier in the thread.
Alan