My 1999s showed "M535" on the option tag. That's "Anti-theft lock 315 MHz". My '97 does not have remote locking and does not have the "M535" option listed.
I think that the tech is correct and your car never had it.
The 696 option is "Porsche CDR 220 Radio, USA". I don't know the 236.
I may be able to help. I have an engineless '98 Boxster parts car with a DME, immobilizer (M535 version) box, and key fob that I want to test. Next week I might find time to pull it out of the parts car and try it all in my '97. If that makes the remote locking work in the '97, you could probably do a similar swap in your car. I'll report back after I give it a try.