Dan,
Thank you for the responce, I'll be adding it to my files.
I must admit thoe that I still feel that the side rods are not quite original. Standard Baldwin practice, from the 1870s through the end of steam, was to stamp all parts with the engines seiral number; i.e. "8-18-C-25" in the case of the Sonoma. This stamp can still be found on all of the Sonoma's side rods and on the Glenbrook (8-20-D-??). While at Railfair '99 I was unable to find any such stamp on the Eureka's rods (You were there when I spotted it on the tender tank, 8-18-C-17 I believe.) While I may be completely wrong, and it really wouldn't surpise me much, I will stick by my thoughts that the rods are "new."
Thanks,
Curtis