Trans leak up front

In 2012 I swapped the -77 318 & 904 for -89 roller cam 318 & A500 & replaced all seals, new frost plugs, engine + trans oils & filters & so on & since then it's been doing fine as daily driver with oil & filter changes...

I was visiting a friend some days ago & he complemented me on my car since he sees it as old & I said "yeah, it's dependable!" & then I was gonna leave & saw a BIG puddle of trans fluid under the car!!!
Drove home fast! Lifted it up, took the plate at the lower front off & saw it comes from behind the converter...

I know what I have to do so no use for comments about that, but I wanna know if anybody has had the same happening to a normal daily driven car in good condition, not a racer, & what had happened?
(I haven't yet got around to start on it)