[alphaphoenix]

I know one was 1964ears: http://1964ears.com/products_customsleeves.html

 

[A Ham Sandwich]

That's the one! I even remember seeing the Coppers on the page as their example.
Now I'm really not sure what to do.  Head-Fi can be overly helpful sometimes and I mean that in a good way!

 

[alphaphoenix]

If you still have love for your MTPG and there aren't any issues, which in my experience is quite surprising, and you bought them authorized so you'll always have the lifetime warranty, then getting the custom sleeves is not a bad route. 
 
Keep in mind, Monster may be out of the the MTPG for replacement should you need to exercise the life time warranty; there may be a good chance you'll get something on their current line up like the Gratitude.
 
Or, you can sell your MTPG for around $75-$120, take that coin and with the $100+ coin you would have used to purchase the sleeve and ear impressions, you now have a lot of options to experiment and work with in the $200-300 range. This range, for me is the sweet spot.

 

[brenttw]

Have you tried different tips?  I just got the MDT and they are fairly heavy too, but i got some Sony hybrid tips and all i have to say is DAMN!  they really do make a difference and they grab your ear canals like crazy!  If i dont take the earphones out of my ear slowly the ear tips will often come off.  Just offering a cheaper alternative to look into. 

 

[A Ham Sandwich]

Yeah I've used the Sony Hybrids and they're markedly better than the Monster tips but the 'phones still won't stay put.
 

 

[JonnyRocket]

Have you tried wrapping the wires over your ears? I had the same problem, the left earbud would start to sag and then fall out. I also modded the large triple flange tips to a double tip and that ended up being perfect!

 

[A Ham Sandwich]

I tried wrapping the wires over my ears but I never got the fit right, maybe it could use more fiddling.  I also tried modding one of the three-flange tips down to a two and still no dice.