One of the slide pins has the rubber sleeve fitted, and it causes the pin to not easily slide. Whether it's due to age, or what... 🤔
I don't know what make of caliper they are, just single piston ones. Likely as originally fitted.
Anyone know if replacement rubbers are available, or is it OK to just remove the rubber sleeve? Thanks!

 

Get a couple of new calipers from your local motor factors be far handier. Their 27 years old.

 

Joe! go wash yer mouth out,! I'd rather repair than replace with ​​​​​​
Chinese Replacement Automotive Parts. (see what I did there..?)
Anyway think I've found a refurb kit on ebay for £8.99, which includes the rubber sleeve, just need to check the number on the casting is the same. 👍
Update: yes, number on casting is 5706, which the slide pin refurb kit covers, so have enough for both sides. £14.45

 

Further to my original post, above, I bought a caliper refurb kit, and decided to do both front calipers. The pic shows one pad from the n/s caliper, which didn't have a sticking slide pin, and the other pad is from the o/s caliper, which DID have a sticking slide pin due to the pin with the rubber sleeve having jammed. Each set of pads were worn equally.

Pic shows left hand pad from caliper without sticking slide pin, 8mm thick
Right hand pad from caliper WITH sticking slide pin 2-3mm thick. Both sets of pads fitted 2 years ago at same time.

 

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Interesting -- sticking/worn pad forced near to disc and couldn't move away??