I have a 1996 Land Rover Discovery and the problem I am looking for the answer is this: When the engine warms up the idle rpm drop from just over 500 to 250 and it sounds like it's about to cut out. I have been told that it may be a vacuum seal, so I was hoping others have had this same issue and could shed some light on it for me. Thanks for your time

 

If it idles normal when cold and then not when hot then I would agree that it is a vacum leak.
Take a spray bottle (like a empty Windex bottle) full of water and when the engine is warm and idleing low spray the bottle all over the engine, if it sputters/stalls then look closly at that area.