Years ago I had an issue with a couple of Ashdown custom cabs - not a fault but something not to my taste. They invited me to their factory in Essex to get them sorted and gave me the grand tour while I was there, getting me to try out all the various amps and basses they had. As far as I know they still open their doors to anyone.
A couple of years ago I had to contact Guitar Guitar regarding a G&L bass I'd bought a while previously which had a dodgy truss rod. They went out of their way to sort it with G&L, even though I was probably out of warranty. Ultimately G&L couldn't send a replacement neck so Guitar Guitar refunded me without any hassle.
Rotosound were great too, replacing duff strings with a whole new set without question. Sadly the fact that I had to do this pretty often is why I now use DR!