Does you temp switch look like this?

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=2AT0J1QHK2DK1AEZ01&year=1985&make=MB&model=300-DT-001&category=R&part=A%2FC+Temp.+Switch

If so, I would not replace it unless it doesn't work. It can be replaced as necessary at any time, as is threads into blind hole on the drier. Also, you won't really need it if you are going to install a manual switch.