Re: outdrive ??
Sounds like you're talking about "gimbal housing access plugs" like the one the red arrow is pointing towards in this pic:
The plugs mean that the gimbal ring had to be removed and most likely replaced, usually because it developed too much play from not keeping the clamp bolts at the top of the gimbal ring tight. The only way to remove the gimbal ring is either to remove the engine from the boat so you can get to the back side of the housing, or drill the access holes so you can get to the bolt from the outside through the holes. The holes are then plugged with the "cap plugs" as you called them when you're done.
It's a very common repair on older (and even some newer) boats. No problem at all if it's done right. Look very closely at the inside of the housing where the steering lever sticks out and make sure there's no sign of a leak there.
When looking at any I/O, you should have someone hold the steering wheel and see if you can move the outdrive from side to side. If there's more than 1/2" to 1" of play you need to find out what the problem is, or it could be very expensive!!!
