OK, well after spending the day playing with this ETRS, I'm happier about it than I was yesterday and as it turns out it's actually an ETRSi, so that's a little bit of a bonus.
I stripped it all down as much as I could (short of dismantling it completely) and gave it all a good clean and re-glued some of the leather where it had started to lift. The 'worn' speedgrip winder turned out not to be worn at all as I just had to tighten the two small screws on top.
I think the previous owner had used it around someone that was doing some decorating as there were fine spots of white emulsion paint on one of the lenses, lens hood, the winder, film back and main body. Thankfully all easily removed with a handy little 'pick' that I had in my toolbox, but it took ages. All the lenses have cleaned up nicely and are all free and functional with no signs of fungus or serious scratches.
I found a small PC/jack lead for it so that I could connect it up to my Godox Xpro trigger to test with my Godox studio lights and it triggers them nicely, so some more experimentation the next time I get a model to pose for me. I only shot half a roll of film today, so I'll try and get that used up in the next few days so that I can develop it to see if there are any light leaks. Hopefully, there won't be.
Overall though, all seems to be in very good nick for its age and today I managed to pick up a winder handle for it on evil bay for £50.00. I thought I was going have to spend double that or more judging by the prices, but thankfully one seller accepted my offer and let me have it before anyone had bid on it.
I don't like the prism finder much, I prefer the waist level finder and was most impressed at how much easier the little magnifying glass helps with focussing.