@Muggins, I'd dropped one of my Weston IIs on a trip back in June and it's been on the shelf for a while; I spent this afternoon "repairing" it, and thought I'd take a couple of photos for you in the process - hopefully this helps. The Euro Master is a bit different, but if I'm right and it is just a repackaged V, the insides are very similar, from what I remember - there's only the bar that traps the needle which complicates things.
This photo represents the only tools and the only point you need to get to in order to solve any issues with Westons, in my experience. I didn't photograph the actual tear-down as there's not a lot to it: remove the nameplate on the back, remove the screws that are underneath, and lift the back from the bottom up; there's two angled metal rods holding the upper section in place that you need to slide the back off, as you can see here on the right:
Take the "baffle flap" out, and there's just three screws holding the front in place; one at the top, and the two long ones you can see in the tray on the right in the first photo. Don't touch the wide slotted screws that are still in place in the second photo unless you have to go further in.
In this photo you can see both how delicate the needle is - don't put the meter face down without having the cover glass in place! - and the reason mine was jamming; there's a scrape line to the right of the solenoid. I presume the two arms with wraps of copper wire coming off the centre are weights to keep the mechanism balanced, and one of them had bent slightly downwards, meaning it was catching on the body of the meter. Bending it back up slightly allowed everything to move freely again.
It's a really simple but delicate mechanism; when I first obtained this meter a few years back, the mechanism wasn't located properly, and that tiny spring in the centre was a bit of a mess. Some gentle coaxing got everything back to where it was supposed to be and it's been accurate across the range ever since.
A couple of words to the wise with regards to reassembly:
First, don't knock either of the circled components if you can help it. This is the zero-point adjustment, and the protrusion on the right has to locate inside the slot on the left. If you spin one out of place, it can be a real pain to get the two to line up correctly again. Don't ask me how I know that.
Finally, keep an eye on this little spring underneath the faceplate; it's what keeps the button for the film speed adjustment in place. First time I took a Weston apart I didn't realise it was supposed to be there until I reassembled the thing and something felt wrong. It was already lost in a shag-pile carpet at that point and I had to do a magnet sweep. Working over a tray and/or rubber mat is obviously best practice, but mistakes still happen!
This was maybe a five minute job at max. Westons are gloriously simple things to work on - much nicer than the Gossen Sixtar I've had on the shelf for over a year and keep meaning to repair - and I'm sure you'll be able to get yours back into shape with no stress at all. Good luck!
