Resurface/fix warping/chipping wood timbers in wood retaining wall/terrace
I have a terraced retaining wall make of roughly 6x8 timbers that were pressure treated. The wall/terrace is 20 to 25 years old and installed by the former owner. The surface of the wood is now chipping and 4 or 5 of the timbers are warping out at the ends by about a half inch. Can I shave down/cut off/sand off about a half inch of wood at least on the warpped ones or perhaps on all so that the old dried out and slightly decaying wood can be removed? I was then thinking of getting sealent and retreating with a few coats to protect the wood from future damage. It seems like the dirt side wood has probably absorbed water over the years and the concrete patio facing surface has dried out and been baked by the sun and shrunken. Hence causing the half inch or maybe more (in some places) warping.
What should I do? I confess I haven't been treating the surface often. (Maybe 4 times in last 15 years.) But I don't want to rip out all the wood and rebuild from scratch. The terrace is about 30 feet long and concaved (3 sides partly wrapping around a pool patio). It even has some steps going up to the next level of the yard built into it.