Also, of course, a mains fuse would not be rated at 32 volts.
P.S: Unless perhaps a previous owner replaced the original fuse with a 32 volt automotive fuse, which might also explain why the fuse that was in there was a fast blow, rather than a slow blow which is what I’m pretty certain an MDA-10 is.
And if a previous owner had indeed replaced an MDA-10 250 volt slow blow fuse with a 32 volt automotive fast blow fuse, I would certainly not find it surprising that changing to a more properly rated fuse would make a transformative difference. And perhaps changing from the SR fast blow you went with to a slow blow would reduce the sonic downsides that you indicated resulted from the change. As well as minimizing the risk that this expensive fuse will blow prematurely.
Best regards,
-- Al