Sony WM D6C crackling noise when fiddling with the Record Level dial

I've got a used WM D6C that works pretty nicely, however an issue I've noticed recently is that if I record from the mic input (haven't tried the line input yet) then, especially at levels of around 2 and lower, there is occasionally a little crackle and audio becomes quieter or cuts out on the left or right channel. If I press on or fiddle with the dial a bit I can exacerbate the effect and even when finding a spot that seems fine I've noticed that recording a whole tape will have a moment or two where the left or right channel will have a little crackle and cut out very shortly.
I remember when taking the thing apart to change out the rubber parts I've seen that there was unfortunately some corrosion around the dial so I'm not sure if maybe it's just a lost cause and I have to live with it. But regardless I would be grateful for some advice on which parts of the Walkman I should inspect and if there is anything I can do other than doing my best to clean the contacts with IPA.
Thank you in advance.

I guess since I'm here I would also be curious about recommendations on settings for recording mixtapes off my computer. Through trial and error I've found that setting the application I record from to full volume (since it's just a linear slider, that's hard to control), setting Windows volume to about 12 and the Record Level on the Walkman around 2 works pretty good. But I'd be interested in the theory behind it, I'm assuming the louder I can get the source (the application playing the audio and the OS output) the better the quality reaching the Walkman will be.

 

Try to clean the record level potentiometer with contact cleaner (Kontakt 60) and turn it from min to max 20 times or so.
However do keep in mind on D6C these potentiometers do also break (if the unit has been dropped), so do check if there are any cracks on the carbon trace PCBs.

Then as far as the levels from PC, first of all there's no reason to use the MIC IN unless you actually use a microphone. That's because you will loose a lot of dynamic range and increase the noise unnecessarily.
MIC levels are very low, meaning you will need to attenuate the signal then re-amplify it, when in practice you can fed it directly to LINE IN instead.
Second, the digital volume on PC should be as high as possible (to get the maximum amount of digital information), but it's also not the limiting factor in this scenario since tape noise & distorsion is high compared to a digital system.
If you have a dedicated DAC with analog volume control, this doesn't matter at all since the digital volume will always stay at 100%.