hey man I've been playing with the TPX since they first came out. (i think my serial number is like 5000). but heres the info your looking for:
personally I have NEVER had a leak... so it was probably an issue with a slight part being a little bit off or lack of grease since that seemed to fix it. My biggest suggestion would be learn how to put the cartridges in properly. Or you can blow o-rings in your marker and screw things up. As for the clip efficiency. 2.5 is about right. I was disappointed when I first shot it and learned that 2.5 is the correct efficiency, but you get used to it and make sure the shots count more. I would really recommend a remote line as people tend to enjoy the marker more... personally I use the Cartridges since I find it more fun.
so basically the TPX is a bit of an air whore... but its totally worth it when you get that rewarding hit on your opponent.