Weird Contra Issue

[Bob-Bob]

So back in June I bought a bunch of games from waterclocker, a dude you may know from eBay. Among them was Contra, which I paid $60 USD for.

I played the game every other week or so since I got it, and now that I moved all my games into my new apartment I tested it out on my Famicom again only to discover an issue I've never experienced before since I got it:
The game refuses to read either of my controllers right. Upon starting the game up, Bill uncontrollably moves to the left as though I'm holding down left on the d-pad. From what I can see, it doesn't matter which of my two NES controllers I use, and this doesn't seem to happen to any of my other Famicom carts.

Is this a known issue? Does anybody have any idea what might be causing this?

[HummerTeam1001]

Is it just on Contra or does it do it on other games too?

If it does this for all games, the controller port might be dirty.

[Bob-Bob]

Well I fiddled around some more and figured out it's not just Contra.

It's actually one of the controllers. Of the two I have, one of them is a little less used and has firmer buttons, while the other is a lot more used and has squishier buttons. For whatever reason, whenever the more used controller is plugged in, be it in 1 player or 2 player mode, the game acts like left is always being held down. It did something similar when I tested it out on Yoshi's Cookie.

Anybody have any idea what would cause a controller to behave this way, and what could be done to fix it?

[HummerTeam1001]

That's pretty weird. Maybe the pins on the controller are dirty and need to be cleaned? I'm not sure if that would help though because I've never had to clean a controller port or controller plug.

[fcgamer]

I've had controllers like this before.  Never tried to repair them, just got rid of them.

[waterclocker]

Probably the 4021 encoder chip in the controller is shot.  I've had a few original Famicom systems with that issue unfortunately.
I still need to try and fix them or swap controllers 

PS: Thanks for the purchase!

[Bob-Bob]

Assuming that is the issue, is there a known way to fix it?

[number47]

4021 IC costs about $3 on ebay. The swap is really simple.