Just to report.
Some of you may recall that Seniorboy has, for many years, had symptoms of residual cat flu - for which nothing conventional can be done really.
I heard about l-lysine treatment on this board and when he was last at the vets (a couple of months ago) I asked his vet about it. She didn't actually know much about it so only expressed interest.
As there appeared, from some research, to be no contra indications, I acquired some powdered lysine and he's been on it for 3 days now. Sneezing and snottery nose have both stopped. It may be coincidence but I give it to you for what it's worth.