Shawn, can you bear a few forensic questions, just for the record:
--Was there possibly a weld of any kind at the break point.
--Was the rubber tube lubricated/filled with grease (pumped in through the tube grease fitting).
--Was there any sign of scoring of the post by the lower rudder bushing.
--Do you think an eyeball inspection of the rudder in place, either by haulout or diving, would have revealed suspicion?
I happened to have my own rudder out recently, for prop shaft replacement, but removal of the rudder is not a routine thing and for the 381 costs $900.
I think you could get creative with some sort of weld repair, but not just welding. I think you'd need to remove some of the foam in the tube, remove the compromised section of the post and insert a machined slug of stainless and weld it back together. But, only if it were welded by a real pro. I wouldn't trust my amateur skills or some random "guy with a welder".
The tube wasn't lubed well, because I didn't realize it needed to be lubed--never noticed the grease nipple. There was some light wear in this area--a few thou.
There wasn't any scoring around the lower bushing but there was a bit of burnishing--no more than a few thou. The bearing and bushing were both lubed, but were definitely in need of cleaning and re-lube. I'm not sure about their condition though--it's a good point--I'll take a serious look at them tomorrow.
On my boat at least, there isn't enough space between the rudder and the hull to really see anything. I think you have to drop the rudder to be certain. You really don't need to pull the rudder completely though. Just loosen up the quadrant and bushing and tap it down from the emergency tiller port. An inch is probably all you need. Then tap the rudder back up and retighten the quadrant/bushing. It's maybe a two hour job. However, you might get some information without dropping the rudder if you use a hardened pick of some kind to score the post to get a sense of the integrity of the material. It might at least tell you if your post is in really bad shape.
I think the most critical part of the rudder post is the portion that's exposed to the sea. If there is an electrolysis issue, this is where it's going to occur. This is also the area of maximum bending moment.
I would have loved the opportunity to only spend $900 and not potentially loose my boat.