Just an update on this.
I've done what I'd say is a part service on the forks.
I ordered new dust seals and after letting out the air, taking off the lowers and cleaning them, replaced the seals. Getting them out was a mission as they were well and truly stuck, and after starting I was beginning to think I shouldn't have bothered, but eventually they came out. I got the new ones in with some grease (I ended up using a rubber mallet to gentle tap them in) and soaked the foam rings in Fox Gold 20wt oil before putting them in.
I then used a little Conpanna fork grease before putting the lowers back on.
What I didn't do was take the "tops" off (if that's the right word) to clean the insides, so I might do that next. But they seem much better so I think I'll leave it for now.
Also, I'd seen this post -
https://www.mtbr.com/threads/switching-from-grease-to-oil-on-a-raidon-due-to-stiction.853706/
but I haven't put any oil in the lowers. I'm not sure whether to do it or not tbh.
If anyone is interested in having a go I got the seals from here, and they threw in a pot of the grease -
https://greyville.com/products/6553-faa169-30-sr-suntour-32mm-upgraded-dust-seal?store_referer=true
All in all a good learning experience, but with hindsight I probably should have got a seal installation tool, but I'd already spent a few quid on the seals and the oil so I decided not too.