1985 Johnson outboard (25hp) water pump ?

So, this week, I tackled changing the water pump in my old-ish Johnny...with the help of the internet and West Marine, I was able to get it all apart and change the pump with no real issues arising (changed the whole thing, impeller, housing, seals, etc, because I don't know when the last time it was done). Made a huge difference in the amount of water coming out the pee hole, so I'm satisfied that all is well....however, I did notice something in the diagrams that isn't on my engine...an "impeller spacer" between the impeller housing and the engine case (either a long one or short one, depending on shaft length). Looks like just a hollow tube that the drive shaft goes through...not sure what it's for and it didn't have one when I took it apart....the guy I bought the boat/motor from had both for many years and used them often and I've had it for a little over a year and probably put 30-40 hours on it with no issues whatsoever...so, what's the tube do?

I think the impeller spacer is suppose to keep water from spiraling up the drive shaft into the crank, causing the drive shaft to rust inside the crank. Older motors had a O-ring near the top of the drive shaft to prevent this from happening.

Here's a pic of one on my '81 25hp johnson...