So I was working on my car the other day, and while I was under it transmission fluid just started draining out. It looked like the old fluid pan gasket had finally cracked, but when I was about to put on the new gasket and filter I noticed it appeared to have actually run down from the vent tube on the top driver's side of the transmission. I decided to change the filter anyway, because I didn't know the last time it'd been done and the gasket looked old. Now in drive the transmission won't shift from first to second. Any ideas why? Did something just decide to break which also made it leak, or was the leaking a coincidence and I just really mess up changing the filter?