The source of water in the bilge?
In an older boat it's anything and everything.
, stanchions, mast
if it's keel stepped, ports
, hatches, chainplates if they go through the deck, locker covers (if they open to exposed lockers), cockpit
drains if the hoses/hardware to them is old, inboard water tanks
and fittings, keel to hull
joints, hull to deck joints,etc, etc,etc.
Oil? Unless you have an inboard mounted auto pilot with a hydraulic ram the engine and transmission are the only other sources. Just a few drops can make a mess and once it sloshes around your bilge and under the floorboards it can take several seasons to get it all out. It finds all kinds of hiding places when the boat heels.
A packing gland should have some water dripping through it when running under power, it needs it to cool and lubricate the shaft.
On most previous boats I've had I was good for about 3-5 years after re-bedding everything on the deck, including the chainplates and ports
. That usually included having to rout out and solid glass the chainplate through deck holes, which are usually a big source of leaks on most earlier production boats.
Stopping leaks is a full time job, I've ended up re-bedding just about everything on my boats on a rotating basis over the years, to me it's just part of spring commissioning duties if you want a dry boat and no deck rot
boat has a 4-108 which are notoriously leaky engines but dependable as all get out, my solution was to put a formed stainless drip pan under it and change oil absorbent mats on a regular basis. I'll address that when I pull it to rebuild
The earlier suggestion to use talcum powder to trace leaks is a good one, just use it sparingly, a little goes a long way, I used to do that on auto and motorcycle engines when a hard to trace oil leak popped up.