Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
I regret hearing about the problem.
I understand what you mean by a roller with lock caps on the end, I think. Would that be a metal rod or metal cylinder, with plastic caps on the end that have protrusions for slots on them?
If so, that part needs to be fit back into the machine, quite simply, wherever is consistent with both where-it-was-when-it-fell-off (since things cannot fall upward), and also consistent with those end caps. The end caps *have* to fit into a hole that will hold them. So the way to find the right place is to leave the metal rod/cylinder and one of the end caps to one side, and with just one end cap in hand, find all the holes that really might hold them.
Then the holes you found that the end cap fits, can be eliminated if
A. they have no other hole opposite them, for the other end-cap, or
B. if the other hold opposite the hole you found, is not at the right distance for the rod/cylinder to fit between them.
If this all proves too difficult, taking the printer to a good Brother shop that works on and is experience in the model you have, would be ideal... they would probably find where to fit the rod in, within a relatively short space of time, and hopefully not charge too much for their manual expertise.
I can locate specifically such shops for you, and their contact information - if you will let me know what your region is, by zip code or by town/city and state. Let me know, if it gets to this point. Thanks.