Assuming you have the "angled" type oarlock sockets, it might help to use longer screws from the top such that they'll go all the way down, through the riser, and get a firm grip on the gunnel below?  I'm just guessing here....

.....MIchael

No PMD builders anywhere near me.

I'm left with the line drawings posted elsewhere here for an idea what might prove useful for reinforcement. Pics of owners' boats would be welcome, showing this area in detail.

If gunwale's the sole support for 'riser' mounted oarlocks, what may help is to add some blocking beneath the risers that's bonded to the upper strake/panel. This would help spread the load the riser's meant to sustain, particularly if proper fasteners are used to take advantage of the greater strength afforded by the blocking. After all, these components are serving to power the craft and crew while being rowed, much as the mast pocket does when sailing.

Functioning as a lever fulcrum, risers' function as foundation for managing forces imparted by the oarlocks above need to be properly thought out for durability.

Thank you, both!   

After looking at some photos of the oarlock risers and sockets on my PMD, I'm wondering if longer screws from the top side down wouldn't get into where the plywood upper strake and the solid wood gunnel meet--probably not the best place for the screws to get a solid grip in helping to hold the riser to the gunnel.  If that's the case, maybe a couple of (countersunk) screws further outboard would help assure that the riser and gunnel don't get separated.  Mine are exactly like the angled oarlock sockets shown on CLC website--search for "oarlock sockets" in the "lookup product" window.

Also, if you're getting some creaking noise, it might be that it's the oarlock socket moving against the riser, not the riser moving against the gunnel.  If the riser itself seems firmly glued down, try tightening the screws and see if the creaking stops.  If you didn't bed those with 4200 or BoatLife or some other sealant, I'd disassemble them and then put it all back together with your bedding compound of choice, making that the screws (1) have a good bite and (2) get tightened down really tight so there's no play.

As spclark has noted, this is a very high stress area, and you want to make sure that the whole business stays together so you don't end up the proverbial creek without the proverbial paddle in a hard chance.

.....Michael