Thanks for all the advice!
I've spoken to my Doc recently who has said that there are as many things to try on sinuses as there are for the common cold. However it seems to be down to picking the technique that works for the individual. He did, though, suggest the menthol crystals himself.
I think that anything that cleras the nasal passages should have a beneficial effect. I've now got a spray to use in emergencies ie: on the occasion in flight when I think it might affect me. Apparently these are not good for long term use.
So if you happen to be in the steam room of the hotel down route, watching someone inhaling deeply, it's proably me
Hopefully one of these will do the trick!