had to be serviced regularly, and was... delicate;
I'm not a fanboy of the Python, (don't own one nor intend to) but you're right in that every few thousand rounds or so, you have to replace the hand. Fail to do that, and the system could fall out of whack rather quickly.
Long term longevity of the MK3? Well all the parts are machine fitted, meaning that after they were made in the mold, then case hardened, they were all placed into the revolver by cheap labour. The MK3 series is a lot more friendly for working on the parts by oneself, however that doesn't mean they're intended to be fitted. The case hardening is very thin, and if you file any amount of it off, you could damage the part. The outer layer is tough as glass, but thin and you are not supposed to penetrate this.
If a part starts to fail, you can simply order a replacement and it'll most likely fit right in. For example, the Mk3 Metropolitan cylinder will fit into the Trooper frame and cycle just fine. All the grip frames of the Mk3 series were all identical as well. However they were different from the earlier V-spring Colts.
The frame of the Mk3 series was glamoured by writers of the day as being the toughest DA .357 around. Do I believe them? They're probably right. I mean I have no worries about the gun ever "blowing up" and if it does have a mechanical failure, I know it'd easily be fixed. Do not dry fire it without snap caps however, as from what I understand, the firing pin can break , and to fix this it requires a pressure mechanism that only the Colt factory was set up to do. Now days Colt will refuse service on their older discontinued models. There is a third party company that still works on the Mk3 series, and they can fix any firing pin issues or send you any newly manufactured part for the MK3 that you so desire. (I forgot what this company is called).
The trigger pull weight is governed mainly by the coiled mainspring, and in my experience there is two main different weights. Mine, and as well as a good number of them, have a very heavy and atrocious trigger pull (probably for Law enforcement). Heavy mainspring. But there were also Mk3s that had a lighter, and smoother mainspring. You can easily change out your mainspring with one of these, if it's too heavy. Personally I wouldn't, as I've heard of light primer strikes with these, and that defeats the whole purpose of double action being reliable.
Get yourself a good thick leather holster, the Mk3 deserves it.
