Old Chateau

Ok, I don't know if I'm doing something wrong or what, but I can't seem to find a Gengar in the Old Chateau on my Platinum. I've tried Dual-slot with Saphire and FireRed (it says to Dual slot with any gen. III game), and I still can't find one. I know it's only a 4% chance of finding one, but I've found wild Chanseys on my other games with a 1% chance of spawning faster than this. Please give me some advice or tell me what to do XD

There isn't really any other way, I've encountered a few Gengars myself when I go there to EV train.
You have a 1/25 chance of encountering one, but don't give up.

4% chance is still better than not finding one at all ^^

Thanks for the advice ^_^. I've been ignoring that place for a while, busying myself trying to chase down Mesprit (who can never stay in one place) and trying out the battle tower (which is awesome). I guess I'll just have to grow some much-needed patience. XD