Considering that the manufacturer is in Japan! Once these housings leave the country they pretty much don't care anymore.
You really can't have it "serviced" as far as I know. Matt, from Marscuba.com was telling me that there is no O-ring kit that he know's of for the buttons.
You MIGHT be able to look for an email address in the manual to see if they will sell you one - but its doubtful, since these cases seem to be designed as "desposible" in a way (cheap price, cheap construction). Don't get me wrong, I dove with my PT-010 housing for 2 years before upgrading to an Ikelite housing. I tooks some pretty good pictures with that housing. But like you I also was worried about the buttons leaking, since the shutter release was cracking (due to my damn pelican case being too small!).
Another thing you might be able to do is contact Ikelite and see if they stock different size O-rings, since they sell controls as well for the home tinkerer.