I had a talk with Steve at PBR a little over a month ago because my Space Odyssey didn't have any 455s in the head. He said that EMs always came out of the factory with at least 4-6 455s in the head. I ordered some of the Eiko bulbs and my experience is the same as others here. Some barely blinked right out of the box and within a week or two, many of the ones I installed had failed. I just found an Ebay auction for some NOS 455s and I ordered 20 0f them. I'll report back as to whether or not it was worth it. From the sounds of some of the other posts here, I did the right thing.
Once I had some flashers in my head, I was really happy at how much better the backglass looked with them in there. Can't wait to see it if these bulbs indeed blink better and last longer. Thanks for the heads up, everyone. Little shreds of advice like this are the things I like most about Pinside. It's always great to find other people sharing this type of info. I would have just kept on buying the Eiko ones without this thread.
Side note, I can't help but be curious about the posts mentioning that the Eiko bulbs used to be better a few years ago. Anyone else feel that way? I know I could switch to LEDs, but I would rather keep incandescent bulbs in my EM. Just personal preference, but if the quality of incandescent lamps is indeed dropping, then maybe a time will come where there won't be any choice in the matter.
Again, thanks everyone for the info on this issue!