A couple of things here. always thought that meteor springs fit hawk pistons better than Webley ones. I took up a Hawk piston To MAG and asked for a meteor mainspring to fit. Alan, quite rightly, pointed out that it was a Hawk piston I had. I told him to try a Webley spring in the piston and then a meteor one (silver streak I think) and he agreed that the meteor was a better fit.
I cannot understand why the Hawk mk1,2 and 3 have the same mainspring, when the mk1 has a shorter cylinder. They always seem oversprung with one of these fitted.
On the subject of the sleeving the transfer port, I tried this after reading Mick,s comments on the B2 and the Hawk earlier this year. Not having a chrono or anything, and having a bit of time to kill one Saturday night, I found a rivet that would fit the breech seal hole on the cylinder and then put the breech seal back in. The pellet seemed to be hitting the backstop harder and the POI moved about an inch to the left and higher ( I think). I tried it on another hawk with the same result. The rivet then fell into the cylinder , prompting a quick strip down. If you are not an engineer, I suppose the easiest way of sleeving is to us some Ptfe rod or similar to make a breech seal and open up the hole a bit at a time.
I also had the leaking cylinder thing with a hawk. I had to unscrew the cylinder end and jaws and use loctite to sort it. When chronoed for me, that had gone up from about 6.5 to 8.8ft lb.