Its had a small leak since I got the boat a few years ago. I've been mostly restoring the boat and it only was on the water for an extended period last summer. 

The leak is small enough that it is not noticable, but overnight the bilge fills about 4-5 inches high under the engine. I'm not 100% sure, but I think the water level stops here as I've never seen it get higher.

I've looked all over and can't find the leak. I even filled the bilge with water and let it sit on the trailer but it didn't sow any signs of reverse leakage. 

I added silicone around the exhaust pipe...no change. The drive shaft packing is good and new and is not the souce. 

I've narrowed it down to 2 possible sources....

1) The rudder packing. I commented on another thread earlier today about what is the correct size packing rope, 3/16 or 1/4? Ill order some to have on hand when I start troubleshooting. It was also suggested in that thread I try tightening the gland nut on the rudder.

2) The rear-most tracking fin is bent about 30-40 degrees. Its on my list of things to do to lightly heat it up and try to straighten it out. It is not noticably loose. Could this be the leak? It showed no reverse leaking when bilge was full and boat was out of water, but maybe that doesn't mean anything. I assume it is caulked with 5200 which I've heard is a bear to remove. Should I try to remove the fin and re-attach with fresh 5200? I'm guessing the rudder is the easier path to pursue first?

3) Its also not the muffler. There was a small crack on the bottom that I have done a fiberglass repair on.

4) Any other ideas?

Thoughts?!!

I don't really think I'd call 4 inches of water overnight a small not noticeable leak. 

Since you already know the rudder packing is leaking (from your other thread) that seems like a good place to start

If you tightened it too much after the repair you could have crushed/damaged the fiberglass enough to have a leak that might be hard to see unless you take the muffler back out to check

Your fin is caulked with some gooey, sticky pretty strong stuff not necessarily named 3M 5200, some people take the screws out and it falls off, some have a hard time 

I would be suspect of the rudder packing.

Happened to me several years back.  Was rafted up with fellow CCFans at Lake Lanier one afternoon.

Opened the in floor ski locker to find it filled with water.  Pretty suddenly.

It was the rudder packing.  

My 93' Sport required removing the gas tank and center rear floor panel in order to access the rudder port. Would think you would have to do that even in order to tighten the gland nut.  

Suggest you buy both sizes of packing rope (not too expensive).  Once you get in there you will have what you need on hand to change the packing.  

The biggest part of the job is removing the gas tank. 

Other than that; pretty easy fix.  

Picture for reference.

A few follow-ups...

1) I may not have been clear in the other thread about the rudder packing...I don't know if its leaking or not. Its just a possibility. I think I will start there. 

2) I am installing a new through hull exhaust port. So I guess I should pull the gas tank to have easy access to both the rudder port and the inside transom nuts?

3) Thanks so much for the picture of the gas tank removed. I've had everything else apart back there before except for removing the gas tank. How hard is it to remove? I've looked at it before, is it just the metal straps and hoses. How involved it is? I'm hoping its a bit easier than I fear!

4) Can you tighten the rudder gland nut without removing the tiller arm or do you have to disconnect it all to tighten it?

1) I do not remember how I determined it was the rudder packing.  Did it in 2013.  Figured it was something that needed doing on my 20 year old boat (at that time).  Yes, it solved my leaking problem.

2) Yes, you would have to pull the tank to do that.  Are you installing an extra exhaust hose and thru hull exhaust port ?

3) Pulling the gas tank is not that hard.  Have to make space to pull it forward.  Remove straps, Fuel lines (one going to the fuel pump and the one for the  vent hose.  Also removed the wires for the fuel gauge sending unit).

4) It is my opinion that if you are taking the time to pull the fuel tank.  Go ahead and replace the rudder packing.  Don't just tighten the nut; you will have to come back later and tighten it again.  Think you are due for new packing on your 26 year old boat.   Repacking the rudder is pretty easy.  Remember to support the rudder from underneath the boat so it does not slide down and out of the port once you loosen it.    

I know some of you guys will cringe, but I'm installing a FAE (Fresh Air Exhaust) thru hull version. 

Good to know removing the tank is not that hard. Do the wires disconnect neatly or do I have to cut and reslice?

The steering cable was replaced by the marina 2 years ago. The mechanic said he didn't remove the tank but would not make that mistake again! I need to ask him if he changed the packing. I'm guessing not. 

What is you guys opinion about leaving vs removing the hullhugger muffler when installing the FAE. I've heard people go both ways. Not sure if I want to find a Y-pipe and remove it or just leave what's there. Thoughts?

Do not expect that your mechanic repacked the rudder when he replaced the steering cable.  Unless you specifically asked him to do that.  And it would be very difficult to do without pulling the fuel tank (if not impossible)