I had the little rubber cover or the USB break off after years of use. Sena does not sell replacements. I found a plug that fits, but has no lanyard. I am going to try attaching it via some fishing line to the remaining lanyard on the unit. Part number for these plugs is A13060300UX0624, found on Amazon, bought a pack of 25 for around $4.50. If I cannot attach it, I will just carry this package in my supplies kit for my bike.
SMH10R USB Rubber Cover Broke Off