So I removed the grille to be able to get to it.
Right.
So one reason why I wanted to service this amp is that at the last gig, it had a strange buzz, which got progressively worse during the night (it was the backline guitar amp of the evening, so it was in use for several hours). Buzes in unsewrviced old tube amps scare me, so I wasn't going to use it until I'd serviced the Dangerous Bits.
Well, I guess I now found the reason for the buzz


Right. I don't notice anything odd when I play at room volume now, but yeah, I can imagine this buzzing at gig/jam session volume; it did sound somewhat mechanical but I could find something that was loose enough to vibrate at the time. Didn't think of looking here.... The chip was lying at the bottom of the cleft between baffle and grill.
Right. So I know it's a dust cap and mainly serves as just that, but also contributes to that "hi-fi" treble of the D130F. I know it's technically possible to just replace them. Is that an easy thing to do, given how they're glued to the cone? Is there a serious consequence to leaving this untouched given how this amp won;t be used for gigs for at least a few months? I have an intact one I could at least in principle cannibalise from my older, broken speaker. Is this where the elusive Black Goop comes in? And, given how the stuff isn't available in Europe AFAIK, do we know an Euro equivalent? Is there perhaps a solid ghetto fix? I can probably live with losing some of those trebles, really

Many questions, once again.