I suppose its possible for block sealer to get stirred up after a couple years.
I have had engines on the stand with the freeze plugs out and ran both a pressure washer, and when I got tired of that, a garden hose in the block for a long time and never got all the block seal, um, stuff, out. The last engine I did where I had to deal with k&w I know it had been in there for several years prior.
I would still check your trans fluid just to be on the safe side. From what you describe it would be a pretty fair leak and ought to be obvious from the trans fluid.
Is the stuff that comes out of the radiator look like rusty water? That's what the block sealer looks like, and it will stain where it contacts almost anything.
Trans fluid would be a brighter red, or more likely a pinkish color, or if the trans is starting to burn up the clutches it could be a darker color, but not really the rusty look like block sealer has. Can't say I've ever seen it stain either, not like the sealer does anyway.