Greg,
the reason for having these o-ring adapters (grooved) is to move the pushrod tubes one millimeter sideways more in line with the cups in the followers. I made 10mm alu pushrods and these would be very close to the smaller bore in engine case where you push down the tubes normally. So I shortened the tubes so as not to enter the smaller bore and have them sit one mm offset as shown in pictures. No real use to have longer tubes except for packing plates under the cylinder and still have a seal on the tubes. So I cannot push down the tubes for disassembling due to 1 mm offset - but I don´t have to ! I just screw down the gland nut and can lift the head as the tubes can change their angle in the 2mm o-rings below, no troubles. And yes, no collected mud on top of the tube seals here I hope.
VicView attachment 35612
Is that addition to the large idler meant to decrease the thrashing noises going on in there?