Ok, big gig in front of 1000+ people now out of the way (the people were there, whether they were listening is a completely different question!), so I finally had a chance to open up the HD 500 to look at those 2 reluctant switches that have been annoying me.
Removed the back screws, slid the floor slightly to one side and back again to access to the inside. As per the video the actual switches are on a pair of PCBs that the run the length of the unit just under the mechanical switches - these only contain the electrical switches and LEDs. Two nuts hold down either end, but the main connection is actually a three pronged clip that forms part of the mechanical switch and prevents the electrical switch from moving.
Just by looking it is obvious that there is no point at all in spraying contact cleaner into the mechanical switches without opening the unit - there might be some value in spraying a little lubricant from the inside pointing outwards just to reduce mechanical noise, but the chances of contact cleaner actually getting to the micro switch from outside is zero - unless you flood the whole thing which is just silly.
I checked the micro switches and the mechanical switches and individually they all worked fine. So I blew around everything with some Air and then did as was suggested and removed the little black plastic bits, then reattached the PCBs, pressed a few switches and tested I could hear the micro switches go click, then turned the HD500 over and powered up into diagnostic mode and ran the switches test. This failed with 5 switches that didn't engage - ok it is now worse than before.
Turning it back over and looking at the ones that were not working I could see that the spring had a significant gap before it would touch the micro switch, so I took the PCBs off again and using needle-nose pliers (round profile) stretched all the springs; they are pretty tough and don't stretch easily. Then I put the PCBs back on again and repeated the diagnostics - this time it failed with 4 switches.
There is still a gap between springs and micro-switches, so I put all the little black bits back again and this time it passes the diagnostics with ease.
That is except for the Expression Toe switch which I have never been able to work without standing on it - during the diagnostics I could get it to switch with some pressure and flexing of the frame. So I had a look at that too:
This is not a micro-switch and the reason why it is hard to switch is simply the mechanical part on the bottom of the expression pedal not making contact - so how to change things so it does work with less pressure? I looked at moving the PCB closer but this is not possible, I looked at extending the mechanical bit under the pedal, but the switch looked as though it might be an electrical circuit being completed by the expression pedal so I couldn't use anything non-conductive. In the end - and with much more confidence about it because I had the unit open - I took a flat file, and with the HD500 upside down carefully removed a millimetre or so from the rubber block under the expression pedal and carefully shook the filings out of the pedal sideways. Then I gave it all another blow with the air and did the full diagnostics test - this time the expression toe switch engaged with reasonable pressure.
It was then just a case of putting the floor of the unit back on and running the expression pedal calibration; and everything is working - I would say just like new, but actually it is better than new because I can use the Expression Toe switch now and never bothered before.
So my recommendation for an HD500 is that switches that won't engage are probably down to compressed springs and are very simply fixed by disassembling and stretching the springs slightly - you will only need the correct size screwdriver, socket spanner and needle nose pliers to fix this and some Air to blow away any dust in the switch mechanicals, and a flat file if you want to fix the expression pedal switch.
You do not need contact cleaner inside an HD500 except if the Pots are going scratchy (not sure how you would notice this except perhaps by the values jumping). A very light oil (even WD40!) can quieten down the switch mechanisms but spraying anything into the switches from outside is pointless.
It may not be the case for every production batch, or for the HD500X, but for my unit I struggle to see how the micro-switches could be damaged by too much pressure and there was no need to remove the black plastic bits. Other production batches may have had changes to the tolerances of the components, and if your switches engage just by looking at them then physical contact may be being made too early in the mechanical switch range and I would consider removing the black bits before the micro-switches are damaged.