It's difficult to find out some information on the Stepwagon RK5 so I thought I'd document my findings here for future reference and to help others.
The RK5 is the 2012 and onwards facelift 2WD version of the fourth generation of Honda Stepwagon (or Stepwgn). The RK6 is the 4WD version. I'm not sure if this information applies to the rest of the Stepwagon RK range.
For any suggestions, corrections or additions, feel free to drop me an email on ben {at} bmcq.co.uk.