The bearings in the freehub body wear, usually it's the outboard bearing as it's where water gets in. It's not a difficult job - dismantle the hub, then the bearing (an industrial press fit) knocks out and you press another one in.
I have exactly that, it's an eczema rash, and itches awfully!!!! It always occurs in the winter, if I change to a drier climate is vanishes within 3 days. I have had it for the last 5+ years, face / eyelids / neck.
I was mildly allergic to one of the chemo drugs (was on ABVD) which trashed my...
@gibbleking fantastic news! I had Hogkins 22 years ago and am clear now after 9 months of chemo. A close colleague also had it, similarly to you it ended up in a stem cell transplant. 6 years on and he is fine - the transplant took a lot out of him and he looked much older for the first year but...
Hmm, external cam QRs really don't allow you to apply that much force. I would try a bolt across that collar first to see - once the waggle test is done.
I absolutely adore touring in Spain, I'll be interested to see some of your venturing into the Vias Verdes.
https://www.retrobike.co.uk/threads/retrobike-touring.258143/page-65#post-3324746
I agree with @bikeworkshop - often bikes leave the factory with an ill-fitting post, often even the post dimensions are wrong or sloppily toleranced. The waggle test is a good starting point.
I have to agree with @pigman - it's easiest to change stuff at the front, even possibly a triple.
If you do decide to switch at the back, for road up to 10 speed any Shimano MTB rear mech up to 9 speed will work fine. After that it's a compatibility nightmare.