Awww, no secret room? But I love the secret rooms! Oh well, at least I know I can play on and I haven't missed something (unlike that ghost that I didn't find, and now it's too late ... grrr).
Anyhow, thanks for letting me know. You are probably right into M5 at the moment and really had to test your memory to remember anything about M4 at all, so well done to you!