If you already know the price then why ask? If you replace the broken lug it is no longer all matching, and loses value there. If you keep it as is, you have a broken part on the rifle which to me would significantly bring the price down. Collectors want all matching and correct, one without the other isn't worth too much. It is why the best examples demand so much, it is a hard state to get.
I once went to buy a Kar88 which was all matching. When I received it some idiot had ground down the protective ears on the front sight protector and I hadn't noticed. Immediately sent back for return as that alone brought that all matching piece which was worth at least 1100$ (at that time) to 600-700$. If it isn't 100% correct and matching it doesn't bring top dollar (unless the buyer is unaware of what they are looking at, which many don't seem to have done their research these days).