I check them on a regular basis after I found one corroded shortly after I bought the boat in 2005. It was the one furthest aft. It appears there is a small place just under the rearmost part of the shaft seal for water to collect. The best clamps money can buy still corrode so I check frequently and change the two rear ones annually, it is cheap insurance. I discovered the problem when I went to check the clamps, one of which just snapped in two. I did check the shaft seal when I had the boat in the yard last year to replace the cutlass bearing and it is in good condition. I keep spares of the correct size clamps on board at all times. I suspect your friends stuffing box had single clamps only. It is prudent to use double clamps on any plumbing that connects to a thru-hull and this also applies to the stuffing box. All clamps should be checked on a regular basis and replaced if any one of them is a cause for concern or showing signs of corrosion.
John Meyer

[quote=pierview]

He spent all night motoring down LI Sound and thru Hell Gate. As he approached Sandy Hook (and home), the clamps around his stuffing box let loose and water flooded in. Serious Mayday issue...
[/quote]
That report sent some chills into me. 

Just a few weeks back, I realized on the third day of our summer vacation cruise that the stuffing box adjustment couldn't be taken up any further and needed to be repacked.   Having done this before -- although not while the boat was in the water -- it wasn't a huge chore (in fact, a piece of the old stuff stuck on the end of the tube and blocked most of the water while I install the new packing).  But the next day, just an hour outside of Provincetown, Cape Cod, at the beginning of what was to be an overnight ocean passage to Maine, I went below to check on the new stuffing and discovered that I had inadvertently managed to somehow break the seal on the stuffing box hose where it joins the fiberglass tube of the hull, and a nice stream of water was coming in. Uh - oh-- not a good thing when one is about to head 50 miles offshore. 

First I thought there was perhaps a minor tear, because tightening the clamps did not quench the leak at all (made it worse, in fact), so I tried strapping a piece of rubber inner tube (from my bike) to it.  No go.  Eventually discovered that slightly loosening the aftmost clamp stopped the leak.  Go figure. Seems as if the rubber tubing gets stiff with age, perhaps?   Anyway, on the list for replacement at this winter's haulout.  

But it does raise the question as to how frequently this hose should be replaced as well (not just the clamps).  
 

Scary Stuff!
That Shaft-Log hose should be replaced every 5-7 years or so if my memory serves. It' snot regular hose. It's 5 or 6 ply I believe.

Here's a link: http://www.catalinadirect.com/index.cfm/product/2585_392/shaft-log-hose-...

I think all CD's shaft-log hose is Buck Algonquin; same with the stuffing box.

Here's the shaft log tube, which has to be glassed in:
http://www.catalinadirect.com/index.cfm/product/2585_392/shaft-log-hose-...

I did a huge repair on mine. Had to repair the tube while she was on the hard. New shaft as well as motor mounts.   

PO let the motor mounts disintegrate which sent the prop shaft grinding through the shaft-log tube over time. 
All. Bad.