Ouch. I'm sorry. That's such a great episode too.
Have you tried the Mercury Theatre
site? They might have the complete version.
I purchased mine on cassette from Radio Yesteryear many years ago and it was complete.
I used to get OTR shows from Napster back before the government shut it down, and I seem to recall that sometimes only part of a file would download but that it would appear to be complete, until you listened to it that is. Maybe something like that happened to your copy.
I've had good luck finding complete episodes, but my gripe has been that so many of the MP3 versions were encoded at 16 or 24 kbps that they sounded too terrible to listen to.
And there are lots of episodes of The Campbell's Playhouse and The Lives of Harry Lime which were cut down when they were syndicated in order to accomodate commercials. Some of the Campbell episodes which originally ran an hour now only run 42 minutes. That's a valid gripe too.