Flexaret VI - removing stuck viewing assembly screw?

In an attempt to rehabilitate my much-neglected rather dim-focussing Flexaret VI, I have ordered a replacement focus screen from Rick Oleson.

The procedure to remove the viewing assembly is illustrated here. However, on my model the screw recessed below the hole marked "Turn wind knob to clear linkage..." in the linked diagram above is thoroughly stuck (I have wound the knob so that the linkage is not obscuring the hole). The other screws came out OK with minimal effort.

Any ideas on what I can try to get this screw loose without disassembling the whole camera (the front of the camera doesn't come off unless the taking lens/shutter assembly is removed, and then basically the viewing lens followed by the rest of the bits and pieces are also removed)?

The challenge is the holes in the front to access the recessed screws are fairly small - I'm using a size 3.0 slotted (flathead) screwdriver to remove the screws, and it *just* fits into the holes.

I checked a couple of hardware stores, and I haven't seen any impact screwdrivers that small.

All suggestions appreciated. Thanks!

I know that WD40 is not recommended generally, but; apply a very small amount with a toothpick to the edge of the screw head and then let it sit for a day before trying again. Then clean up the area with a Q-tip to remove as much residue as possible. This has worked for me a couple of times on very small screws.

Thanks, I tried the WD40, and the viewing assembly did come apart, but it appears my persistence twisted the screw head off instead of loosening the entire screw Must be really, really stuck. Oh well, it's not a critical screw anyway, and it accomplished the same thing in the end.