When I spoke of the Mainspring I should probably have said the Hammer Spring.
The older 357 valves are not quite the same as the more recent version but these like almost if not all internal parts should interchange as far as fitting into the frames.
Some have already tried the newer valve in the First variation revolvers, and posted that performance was not as good as it should be because they had used the hammer spring that came with the first variation. It was suggested that the spring of the vigilante is stronger or snappier giving a stronger strike to operate the valve properly.
It could simply be that the older 357 springs have gotten a little weak with age.
I have two of the older 357 and each has a hammer spring that is a bit different in appearance from the other, though I detected no noticeable difference in strength of the springs.
The Vigilante valve seems to be an improved construction and stated velocity seems higher than I've been getting with the 357 I successfully resealed and got to working properly.
Velocity is pretty good as is but I'm sure the Vigilante does a bit better in this department.
I much prefer the classic Python type styling of the older 357, which is why I obtained two of these that externally as in nearly new condition with only the most minor wear to the original finish.
I have three freshly resealed 38T pistols , two in .177 and one in .22, these are my favorites. The 357 revolvers are less refined , both less accurate at 20 + yards and lower in velocity, but are excellent backyard plinkers. They have an advantage in being able to use the much cheaper steel BBs.
I ordered some lead BBs to see if accuracy improves.