The flash unit isn't covered by a lifetime warranty since there's a lot of wear and tear on them and they can fail with normal use. I'd check those connectors and wires as well, I thought my Tiger I flash was bad from the MFU since the unit worked in other tanks, but never had the downtime to send it back to Tamiya, Then one day when I was doing other maintenance, I found it was just a shifted pin in the connector and everything's fine now.

You can get the crimpable connector ends (or entire housings), it'd be a good idea to be able to replace things like that since they can break with normal usage. We all know how cramped the interiors can get and wires can be pulled loose.