It is nice that you got the worst of it out with the vacuum, that is what worked for me on one of my old m60's. The little dimples won't affect the sound, this is just a cap and does not affect the sound.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85