So, I got a new OEM vacuum tree and a Reinz 978111 o-ring. I put the o-ring in the groove on the vacuum tree, but this thing is way too big to fit into the intake manifold. I mean, the vacuum tree itself just fits into its hole. Has anyone else had this issue?

 

I had it last week. Broke my vacuum tree while doing my PCV replacement. Ended up temporarily plugging the hole where the 'branch' broke off with a sheet metal screw and taking a cap off another 'branch' and using it.

Once I got a new tree and o-ring from FCP, as you say, the o-ring didn't fit. I was able to *carefully* salvage the original o-ring off the original vacuum tree and use it on the new tree. The original o-ring is flat, not rounded, and fit very snug back into the intake manifold.