Can anyone shed any light on this? How common are the problems?
The problem is usually folks don't bother with PM until its too late.
Any item bolted or fastened to a wood cored location only lasts as long as the sealing goop keeps out the water.
The use of Balsa instead of a better core material lowered the initial cost of the vessel, but it gets paid for in extra maint in PM rebeding much of the boat hardware every few years.
A teak "deck" overlay adds to the problems of core rot by having hundreds of screws puncture any fiberglass on the core.