Very hi-tec, soaked in warm tea for an hour and then left to dry but not quite what I was after so repeated the process.
Looking far better now, I've considered one of these in the past but did not like the look. Yours has aged perfectly so better reconsider. Have you used a speed up trick and where do you buy them again as I've long forgotten? [Edit]just seen your further reply which answers the first question.
Here's the strap source: http://af0210strap.com/ I have a couple of their khaki straps and a couple of their olive straps. I think they're planning to do a run of black as well.
Omega 6b/542 58 issue bought in the 1980's by the previous owner at an RNZAF military surplus auction. The dial and hands were possibly changed by the RNZAF. Dial is the thick anti magnetic type.
My treasured Smiths 6B from 1968. Just back from service and a new leather one-piece RAF style strap: