Just a point (not to be pessimistic) but have you checked your mast step to be sure that there is no downward movement? It could be the alternative to the shrowd's stretching. As for the shrowd, we would expect that the steel will perform within the elastic limit ( ie: it stretches under load and then returns to it's original length) but if it stretches under load and does not return, it is performing in the plastic range and this is NOT where a designer wants the shrowd to perform. If the shrowd continues to stretch, you are starting down the path to failure at some later date. If you replace the shrowd, I would consider a slightly heavier shrowd. I hope this helps.