Thanks Jason...but I thing you may have misunderstood. The exterior wood trim is very narrow, and Pella calls this narrow style of trim "brickmold". I'm told removing the top and sides wouldn't be too much of a problem, but removing the sill would be. And then there's the question of what to replace this with! Any of the engineered woods won't do because of expansion/contraction issues. So we're back to wood. Use pressure treated?? and mill it to match the original style?
This is not a unique problem...many of the windows built about that same time are exhibiting similar failures. IS ANYBODY OUT THERE DEALING SUCCESSFULLY WITH THIS????