Hi Rob,
Expect to replace at least two seals every year. They seem to last between 6 months and three years in my experience. I’ve replaced the cylinders but no difference.
Banisters have seals. Don’t use NOS ones.
I find that the first time I run my Saladin after winter, all is OK. But within 24 hours two or more will be leaking. Over the years you will become very proficient in replacing them Now takes me 20 minutes per cylinder and half an hour to bleed the system. I am trying a difference type of seal on two of the cylinders made from polypropylene(??? Spellin). So far so good, but they have only been on for two years. If they last another 3 I will have the other 10 cylinder seals made from the same stuff.
Unfortunately they wont reseal themselves, just get worse.
The Saracen and Ferret brake cylinders however don’t seem to have the same problems.
Have fun..