I know the 4006 started production in 1990 and still is today. That ser# I don't know.
This gun was manufactured in 1991, according to Smith and Wesson headquarters.
250 or so
Email Smith & Wesson. They keep good records and and usually responsive to questions.
You must call S&W. SN goes beyond published data.
100-460 or so
Take it to a gunsmith
Call S&W and they will tell you when it left the factory. It could have been made anywhere from a week to a year before.
100-425 USD or so
500 give or take
Not a user-serviceable part. You need to see a gunsmith.
@1990. You will have to call S&W to narrow it down further
You can request a owner's manual for free at the S&W web site.