From my experience with sticking spring-loaded 510s, you have one of 3 things going on...
1) you did get juice down there (many tanks do in fact leak some juice/condensation from the 510) and over time it got gunked up and now that gunk is stopping t pin from springing back up.
2) The insulator around/the pin is damaged enough that it prohibits the pin from moving freely.
3) The spring or the hole 510 mechanism is simply just worn.
For #1, the first thing you can do (and I know this is going to be controversial to some people but it has worked for me) is to put a drop of 90% or higher isopropyl alcohol on the 510, let it sit, then get a qtip and clean it out as best as you can while pushing on it repeatedly. If this seems to have fixed it, let it dry well before you fire up the mod again.
For #2, well, not much you can do unless you have something that you can use for an insulator (this is why I save all my spent factory coil heads, those things have seals and other parts that can be used to fix stuff). I don't know what size you need, but
FT has 510 insulators for eGo batteries that I have used on other mods and even 510s on tanks. This of course will require you to open the mod to see if you can then disassemble the 510 on that mod to even be able to replace the insulator. This can sometimes be done from the top of the mod without opening the mod, but not usually. If a bad insulator is your problem and you think the ones at FT might work, I can send you a couple. Of course, if the 510 cannot be disassembled, then we come to #3.
As for #3, nothing you can do but replace the 510 or trash the mod. Fasttech has many 510 connectors.
Here is my favorite one - you have to buy 2, and it's worth it at just over $3. This of course will require some drilling and soldering. But of course, which 510 you buy depends on how much room you have inside the mod. You'll have to open the mod up to see if you can even buy a 510 that will work in that mod. It may not be worth saving the mod though, only you can answer that.
It can be done. I have done it. This was back in the day when they used brass threads on mods and it stripped so I replaced the stripped 510.
Here's the mod without it.
