Help! Mysterious Leaky SYE Housing.

Okay so its not so mysterious, but I installed an Advance Adapters SYE kit and Tom Wood's Driveshaft this past weekend and everything seemed to go very smoothly.
Well I filled the T-case up and took it for a test drive, everything went fine no leaks and shifted through all positions easily.
I was worried I might not have enough fluid in the case because I had the front jacked up when I filled so I went back underneath and pulled the fill plug again.
Low and behold it seemed like the fluid was well below the fill hole so I topped it off up to the bottom of the hole.
I drove to work this morning and took a look underneath when I arrived and their was ATF dripping off the case that appeared to be coming from the speedometer housing.
So I am wondering if I overfilled the case or if there is just a bad seal where the speedometer housing goes into the Advance adapters Tail housing?
It also seemed like the tail housing wasn't machined properly when I reinstalled the speedo housing because it didn't really seem to seat properly in the tail housing.
Anyone else have this problem or a leaky Advance Adapters SYE?
How filled should the NP231 T-case be?

Thanks,
Steve

You know, I know that I ripped a tiny chunk off the o-ring when I removed it I just didn't think that would affect the seal that much but if this a common thing then that has to be it.
I think I will also try to put a little more Blue Silicon RTV on the seal as well as the AA instructions suggested. First time around I put a little but I don't think it was effective.
Thanks for the heads up on the O-ring should have thought of that first, usually the most common reason for a problem is the likely one.

I assume you mean Sears hardware has the O-Rings? Would I find them in the hardware section, automotive or plumbing do you think?

Yeah, I had it lifted 2 inches, and just put another 1inch of shackle and spacer lift so it was time to add the SYE.
I am gonna swap the speedo gear with the correct one for 31s and 3.55s now since I just read the "Truspeed" post and replace that O-ring and I should be good to go.
I would like to do some light trails soon, no mud, no rocks, I have learned that they both break things too easily and I don't have a fat enough wallet or another vehicle to handle that right now.

Yeah, yeah, ha, ha very funny!! Let me clarify, no deep mud and no rock crawling.
I've only got one vehicle, a nice looking, good running XJ so body and engine damage are not my type of fun.

Actually I like long drives down dusty tree lined....driveways, hahaha!