It's 3:30AM and I finally managed to successfully flash my first WP-34S!!!
Opening the machines was quite easy, soldering the caps less so. They don't look pretty at all but I hope they still work as they should. I went for "the works" and did the IR diode as well but then found that I had used too short a cable to actually close the calc. When I tried to remove the cable it took the R18 contact pad with it, so I used the shell for the second WP-34S and the board will be the "IR-less machine". (Any suggestions if there is a way to remedy this are welcome, of course.)
Flashing with Flashwp34 worked on neither Mac nor Windows but MySamba did it on the first attempt (with me being quite nervous about having a bricked machine....).
On the first machine the LCD dropped out of its frame and I did not realize this and tried to reassemble it with the screen slightly angled and its edge pressing against the frame instead of being within the frame. This caused where alarming black spots to appear on the display and it took me quite a few attempts at closing and re-opening before I found out the reason (I admit I'm not an engineer).
Now it seems the IR cables push the shell away from the board a bit and the pins of the flash cable don't seem to reach the board as RESET has no effect. I guess I'll have to open it again to see where to move the cables.
Any hints on the best routing to avoid pressure on the LCD. I seem to see very faint shadows on the LCD where the cable runs now (it's a 0,15mm2 cable, the thinnest I could find).
Sticker Time tomorrow but now good night!