Hello Martin,
that uchiko is not so good to use to clean fine blades on a regular basis seems to be common sense, nowerdays. I can remember an article from the 1950ies or 60ies in which a then Japanese sword authority advises collectors to clean and treat blades with uchiko very intensively. Either he based this on the fact that many blades he might have come across in the US were covered with heavy machine oil by ignorants, or he wanted the people to ruin their captured swords on purpose .
The first time, I watched someone using alcohol on Japanese blades was while visiting a Japanese dealer in Tokyo. He was wiping off a blade with some liquid and I asked him what secret solution that was. Alcohol, it came out!
It works really well, especially if you aditionally, carefully wipe the blade off with a micrifiber cloth (german: Mikrofasertuch). Do not employ too much pressure!
90% ethanol or even conventional methylated alcohol (german: Brennspiritus) is technically fine for this application. Make sure that all liquid that could contain a rest of water is entirely evaporised prior to resheathing the blade into the saya. Especially watch the part covered by the habaki! The chemically purest alcohol available is "spiritus absolutus". Your pharmacist will like you when you ask for this.
Uchiko I use myself only on my iaitos after training. It works well to remove the sticky sweat from the mune. If you use a less precious Japanese jitsuyo-to for training with a less elaborate polish, uchiko will be fine for the same purpose. Another reason to use uchiko is when the blade is obscured by human debris such as fat, bone, blood, tissue..., after a sucessful combative encounter
:lol: . Having sayed that, this will be unlikely the case, will it?
Cheers, Dieter