Hi Peter, Have you taken old master cyl apart yet? I've not been involved with too many master cyl, but every one has had rust/corrosion inside.
I put LF Harris stainless master cyl on in each case. Some are a few years old now. Mine is 6yrs old on front brake. All are still working perfectly.
The LF Harris stainless is easy to come by in USA/Canada & a good choice in my experience. I've gotten master cyls from Bonneville Shop.
The adjustment of master cly is critical regarding the feed port opening relative to piston position. Read over manual
& practice with old cyl. Once you see what you are trying to accomplish the adjustment will be correct & successful.
The bikes I've been involved with, owners want to keep stock. They've have used factory made stock type rubber hoses. I used stock type Nelson brand on my front brake hoses. Again all have worked well. Stainless braded is good too, depends on what you want it to look like.
These are the exact hoses I've used & have worked well, fit well. Made by Nelson. DOT approved. This is the only brand I've used. Lots of places sell this Nelson brand. It says Nelson DOT etc on hose in white ink. Shop for what is best place to buy for Canadian resident.
Last few I got here: https://vintagetriumphsupply.com/search?type=product&q=brake+hoses
On a side note I see Bonneville Shop is selling stainless master cyl. in 13mm (one mm smaller piston dia.). I've only ridden one T140 with front 13 mm master cyl & it was a huge improvement in feel & effort. I don't know about the rear. But something to think about. There has been some threads regarding 13mm on rear also. It is said feels better. I've ridden a few T140 with normal rear cyl, but never a 13mm rear.