Entry door adjustable threshold
I've got a Pella fiberglass entry door (approx 6 years old) that has an adjustable threshold. The four adjustment screws will each turn, and the threshold moves accordingly, but as soon as someone steps on the threshold it drops to the lowest position leaving a gap beneath the door. Apparently the screws, or the mating parts (nuts?)are essentially stripped. Are the threshold components replaceable? If so, how is it done, as simply loosening the screws does not seem to 'release' the threshold cap. I appreciate any suggestions.