I still have the very first weathering job I ever did - an Athearn GN caboose.
It was pretty much a "total failure" in terms of being able to actually use it.
I still get "red" when I remember the jeers I got at the layout when I
"proudly showed it off". I especially like to haul it out when I'm helping a
buddy learn how to do weathering (as an example of how not to do it).
At least one of the reasons why it was a failure was because I put it
behind a train of unweathered cars ... but the level of weathering was
"seriously over done" ... *G*.
HOWEVER - the techniques I learned in that weathering session (I was
being taught by someone who was a very skilled military modeler) - are
still with me and very much "in play/in use" to this day.