Merc 115 Water Pump Question

[gman1001]

I'm prepping the 18' SC for the season and attempting a water pump replacement. I've done it before on other engines - just not this one. Hoping someone here knows a bit about merc lower units. (specifically water pumps)

NOTE: I have the Official Merc Manual for this motor.

HP: 115
CYL: Inline 6
Year 1988

I've attached two pictures of the existing pump on the lower unit which is on my workbench & a parts diagram of the pump. I immediately noticed that their appeared to be two missing parts.
1) MERC Part #: 38970 - Rubber Seal water inlet
2) MERC Part #: Guide Sleeve water inlet

You can see these parts in one of the pictures listed as 25 & 35.

I noticed that there appears to be a tube that might line up with the water inlet on the pump that remains in the leg of the motor. I gave it a little wiggle and it doesn't really budge. Could this be the water inlet Sleeve?(part 35 in diagram)

The telltale on the motor worked fine the one time I ran the motor. the water at idle didn't gush out but kind of chugged. So I know the pump was working at least a little.

Any advice thoughts much appreciated...