speedometer/odometer head replacement

[Jo-Ski]

Hi, folks--

We have our '83 FC '35 RB in at a big truck repair place for some fixes. The mechanic has said that the speedometer/odometer head need replacing. Has anyone done this, and if so, do you have any useful advice/info on it, please, that we might be able to pass along to the mechanic? They're pretty knowledgeable at this truck place, of course, but you folks probably know more about any specialized info/subtleties of the matter.

Many thanks in advance (and I did search the archives beforehand, but did not find much on this topic)!

Best regards,

Jo-ski and Stew

'83 FC 35' RB

"The Bird Abides"

Blaine, WA