37xx OEM supplied charger doesn't have a user-replaceable fuse Loly, just an internal fusible link i think.

I'd try again with a dedicated aerosol electrical contact cleaner, it's more effective than using only isopropyl alcohol. Another other possibility is that either the mount's usb socket or the charger lead's usb plug is faulty or just dirty. Same for the car's lighter socket and 12v plug end of the usb lead. Did you clean all them as well?

If all are clean and you have access to another unit try a different mount and/or a different charger. You may be able to isolate first which one of yours is the problem [if at all] by gently wriggling the connections under current while the vehicle isn't running. Also test the lighter socket with some other gadget, maybe it's making and breaking.