Printer always jamming on 2nd tray

I would check the back cover, as a lot of printers use a special rear cover for duplexing - the exception is 110 lb+ printers with duplex support that require active duplexing like the MS8 and MS9 series, as well as the subsequent CS versions. Check for things like stripped gears or a loose panel, to start - if you do not see anything obvious, you may have a bad duplex assembly or a damaged paper eject. Here is a link to the SM: https://www.laserexpressinc.com/manuals/...

Brother Dcp 9030cdn L3510cdw L3517cdw L3550cdw L3551cdw Hl L3290cdw Mfc 9150cdn 9350cdw L3710cw L373

It's deep in there on this one :-(. Not a quick job to replace. That said outside of the large commercial tier printers like the MS8 and a lot of the higher end CS units, this is normal - most consumer printers aren't built such that you can pull the duplexer out in 5-10 minutes and replace it.