With advanced printers like your Brother colour laser machine you need more than toner cartridges to ensure its continued operation. You also need essential maintenance items like the original Brother BU-223CL transfer belt unit.Why entrust the running of the Brother MFC-L3770CDW (and all other compatible printers) to anything but a genuine BU223CL transfer belt unit. Products produced by the manufacturer of your printer work flawlessly with your machine and the Brother BU-223CL transfer belt unit lives up to the companies reputation.If however you should ever have any problems with the BU223CL transfer belt unit, Brother offer a direct warranty, but this is very rarely needed.