THe B&M kit I installed on our black TRD Taco reuses the factory metal gasket and then you lay a bead of silicone around the billet spacer to completely seal everything from the elements as good as stock.
You can see the factory metal gasket inside the purple spacer here...
If that is the way you installed it you are going to have two holes that will let crap into your expensive tranny.
See the left side of the plate and the machined lower area? There will not be any seal in area near the bolt holes. If you look at the underside of the shifter assembly, you will see that there will not be any contact at all between the shifter assembly and the spacer plate in those two spots.
You are also going to find that the bolts on that side will come loose and if you tighten the bolts to much it will just bend the shifter assembly plate.
The problem is that spacer plate is also used on a Jeep product and that recessed area is needed for some bracket that gets bolted between the shifter and the tranny, but on our trucks there is nothing to take up that space and there will be no seal and it will leak and let crap in.
I have spoken to B&M about this problem and they seem to think I am a nut and don't know what I am talking about.
Anyway, do check it out on your truck and if you are seeing the same problem.
One thing I did for a customer, was to put the metal gasket plate thing on top of the spacer plate instead of under it. That will cover the gaps and make a better seal especially if you put the RTV in the right place. Then I made two spacers like washers that go where the bolts are that are the same height as the recess area and now the bolts can be properly tightened and they will stay tight.