Bellows replacement, frustrated

[J2ky2k]

Hi all, this will be somewhat a long post, sorry. 1988 170 classic, alpha one, 3.0.
Boat began taking on water, not much but enough to be concerned about. Inspected and found exhaust and shift bellows bad. Bought bellows kit which included gimble bearing. Disassembled and decided to also replace lower unit water pump, lower shift cable and u-joints while in there. Found what I would describe as a "flapper" just laying in the exhaust stream. What is it and where did it come from? Also, new gimble bearing doesn't seem to have a lube hole. Is this a sealed unit that position doesn't really matter? Another thing, the bellows kit came with 2 different exhaust bellows, one smooth, one ribbed. One better than the other? I have researched utube and such, all it has done is confuse me. Is there a definitive site for answers that I'm not finding? Any help is greatly appreciated. I've been an auto mechanic by trade most of my life but boat info is MUCH harder to come by. Thanks again for any help!