i've read that once the volume knob on the exquisit head unit goes kaput it impossible to fix unless a replacement part is sourced...

NOT!

i managed to open up the knob component... you'll first have to remove the face plate from the HU... its held by four plastic tabs, you can see these from the outside... and one screw under the HU. 2 torx screws hold the PCB to the faceplate, (i used a small flat blade screwdriver to remove the torx screws)
you have to remove the black knob before you can remove the PCB.

Once the PCB is off you can now see the dial assembly, you can remove the top part by prying close the 4 "Y" shaped prongs holding the cover down. don't use too much force, you don't want to break off these prongs coz u need them to close the assembly later. Once off you'll see a wheel with embedded contact serrations/teeth... clean this...
you'll also see the contacts attached to the PCB, clean these too... to ensure contact with the wheel i carefully pried the contacts UP (outwards, towards me) just a tad.

put everything back... it should work like new.

you'll know what to do once you have the knob assembly off... the main thing is knowing that its possible to open up that knob thing by dealing with the "Y" prongs...

__________________

85 190E 2.3(SOLD)
86 230E (-->300D) sold
87 300D (-->300TD) sold
68 250S w/ a 615 and manual tranny (RIP)
87 300TD (SOLD)
95 S280 "The KRAKEN" (Turbo 2.9 602 transplant) traded
86 190E 2.3... current project