Dude!! Thank you so much for this thread. I had been looking all over the internet to figure out what my problem was. I'd just figured out that the 29 spline conversion is what my problem was; however, I wanted to do more research before I banked on that conclusion. As far as I can tell, you're the only person who has figured it out and posted about it.
What is really confusing is that most other places say that the pinion seal on the 27 and 29 spline master install kits are the same for the Toyota 8", which gets really confusing. I am going to call Yukon tomorrow to figure out what is going on.
Here's the difference in specs I found when looking at pinion seals via O'reilley's:
Specs are almost the exact same but the 29 spline seal has a 0.2mm wider outside diameter, a 3mm wider inside diameter, and a 3mm wider shaft size.
To preface this: I run the 29 spline Yukon conversion kit paired with Yukon 4.56s and G2 master install kit. I had some play in my diff, so we swapped all the bearings with new a new G2 master kit. My guess is, the G2 kit is made for a 27 spline, which didn't agree with my 29 spline pinion; therefore, I had a leaky pinion seal. Because I had that leak, I swapped in a new 3rd gen seal from O'reilley's, which is profusely leaking now.
After hours of attempted research, I am now at your post... Keep in mind,
East coast gear supply says their master kit is compatable with either. Yukon has one section that has a master install kit for
-02' and down Toyota 8", which would be 27 spline; however, it also says it's compatible with 4th gens, FJs, and Gxs.... I'm not sure if that's a copy & paste thing or what, but it's confusing.
Long story short, thanks for this post!