why? the russian 91 also leaks from the bottom too, shares the same trait with the kayfun lite. Depending on how much you're getting it for go for the kayfun lite plus instead.
mechs are just an aesthetic and feel thing. But even though they all look the same you need to consider:
1. Thread quality
2. Switch quality including ability to add optional magnets
3. Locking mechanism
4. Quality of housing
5. Quality of contacts ( brass/rhodium/palladium plating is less prone to arcing, which is when your firing pin hasnt quite made contact but the current bridges the gap anyway)
6. Air flow if using bottom fed attys like a Boge
7. Adjustable top and bottom pins
8. Resettable Fuses
9. Style
If you want to have the style with the ability to have vv/vw you can get something like the hydra
http://elcigart.com/en/all-products/27
Thats the thing if i can get the Russian for a good price then ill buy it but if not ie he wants too much money for it then ill either get the rose or KFL plus. Definitely want to get another atty though. Ive all but put my protanks away as i wont be using them again i dont think especially after discovering the joys of micro coils and wool.
As for the mech mods??, those hydra's are nice but i think id rather wait for the GP paps x tbh...something about it i like. If i dont get on with it then ill just sell it simples.
On another note my KFL no longer leaks, wrapped some pfte tape around that screw and all is well so far. Easy fix rather than having to faff around with tiny o-rings.