DSG won't engage reverse on a slope

[McDoof]

Having a bit of an odd issue with my Passat. I have a fairly steep driveway. I can happily put the car in reverse on the flat section at the bottom and it will reverse up the hill without any problems. (better than my old MK5 Golf used to be) However, if I stop the car part way up and then change into D to move forward and then back to Reverse, it will not engage the gear. Just revs freely. Gives me a flashing R on the dash and makes a few clunking sounds. Nothing very loud, but audible. Sort of like the sound the DSG makes when going through the adaptation process.

Rolling to bottom of the hill, turning off the car and turning it back on fixes the issue. There are no other DSG related symptoms when driving the car any other time.
Really only when pointing nose down or with the left side of the car on the downhill.

I'm thinking it sounds like a DSG fluid level issue, but there is no easy way to check my fluid levels. Any other ideas? Could this be the beginning of the end of my mechatronics?