MB Transmission Service Tube

I'd like to service the transmission myself on a 2014 E-250 4 matic.  Upon examination there is no service tube to put the tranny tool into to get a level reading, there is a plastic blind cap on top of the tranny where the tube should be.  Can I buy a tube to access the transmission and install?  Rahaal says no and wants $500 to flush / fill for 40K maintenance.  HELP