It's not the done thing around here, but I put my HM5 pads over some L-Cush pads on my MS1s. They actually dig deep and have a very satisfying bass. Most people are adamant that pleather and Grado don't mix, but my experience couldn't be further from the truth.
I can always pull out the other pair of MLs to check if they're defective, but I highly doubt it. I'm well aware that these are finicky with placement, but I'm quite capable of putting them on and getting a seal. I think it's down to two things. A) The drivers need to loosen up a bit and B) The MS1s actually have very good bass when it isn't all leaking through the airy foam pads, but few people actually try anything other than Grado-sanctioned pads. No skin off my nose if no one believes that my MS1s currently have better bass than these.
A) The drivers do need some burn-in. I think you will be quite surprised at what you hear after 50 hours.
B) Okay. When you talk about good bass, are you referring to sub-bass or mid-bass? How does the bass compare when you use a Grado-sanctioned pad?