A common problem is that the grease in the shifter becomes solid, what influences shifting up. It won't do anymore. I always solve it with removing the housing of the shifter. Make the tiny bits inside go again with oil etc. It is another feel than a stiff going cable however, so I doubt you are experiencing is the same issue.
Thanks very much for all your help, it's very much appreciated.
I'll have a go at the RHS shifter tomorrow. I've had this issue once before and the last time I managed to sort it out so hopefully, I'll be able to resolve it. The new cable has made a big difference but it's still not quite there yet.
Even though the catalogue that I can view is in Dutch, I can now see there's a few more changes than I originally thought. Some of the others I have seen have an English translation with them; maybe I can find a similar one.
The Seat Post, Stem and Handlebars are different from the catalogue but they may have changed over the life of the bike and they are genuine Koga; I know that there was no set specification with these at the time.
The wheelset is the most obvious change that was done fairly recently with NOS rims. A seriously expensive upgrade but the guy I had it from has owned it from new. I've never owned a set of these in 700c but the quality of them is superb.
It's a completely different ride and set up to that of my Koga Miyata Balance. It feels and handles more like an Audax rather than a tourer. I've fitted 35c Schwalble Marathons due to the shocking state of the roads here but it would probably be even swifter with a set of 32s or better still if you're fortunate to have nice roads, Mondials.
I chose to replace the truly awful Alivio chainset with the Stronglight one as seen in the pics. Un beknown to me, this posed a real issue with BB size. and a 127 mm was needed in the end. A lot of trial and error, blaspheming and sweat, I've never replaced a BB so often! I thought it would be fairly straightforward as this particular chainset doesn't require a dedicated Stronglight specific BB. How wrong was I but alas, I got there in the end.
I do think it was worth it though as personally, I think the ratios work much better than the original smaller MTB setup as imho, it spins out far too quickly for this type of bike with the original.
So, after new tyres, a new tube, new cables, new Shimano BB, new Shimano ceramic brake pads and a plethora of small adjustments, it's all sorted.
When I first got it, it had standard brake pads in it which although they would work, the squeal from them must have been horrendous.
The grips have been replaced with the genuine Koga ones which are very good.
I still have the original Koga rear wheel bike lock but it was much easier to work on with it removed.
I do wish it came with the original front rack though.
I particularly like the addition of the pump braze-on underneath the top tube. Sad I know but sometimes the little things make all the difference.
Appears my m8 who owns my LBS was nearer to dating it than me ! I said @ 2001 - 2003 but he said late 90's.
It's in truly amazing condition for it's age.
Finally, after much ado, It's ready to go to a new home.