Estimated value of a Winchester 1912 20 gauge, 2 1/2 chambered, serial number 20780|Winchester Shotguns|Forum|Winchester Collector

I am trying to find a legitimate estimate on the value of my grandfathers gun that was manufactured in 1913. Model 1912, 20 gauge, 2 1/2 chamber, original stock and forend. The butt place I am trying to find a replacement for, it had been in storage and the bottom of the stock had slight water damage. I sanded it lightly, and lightened the darken shade and re-oiled it to give it a good shine. I really don’t think I would ever sell it, it’s very sentimental to me. Just curious as to the value. Had slight spots of rust on the barrel I was able to remove, without a problem. Anyone with any information on an estimate of the value or a good place to get a replacement butt plate. 
thanks