I'd agree that the various Rotax two-stroke found in the
Pik20E, DG400, DG800A are (generally) reliable.
I co-owned a DG400 for many years; nothing engine related
ever failed. In all those years it failed to start just once when
the pilot forgot to turn on the ignition. Hard to blame Rotax for
this!

I have also owned a DG808C with the Solo two-stroke. A brief
internet search will tell you all you need to know about this
two-stroke. Oddly the different Solo in many "turbo" gliders
seems to be very reliable.

As Dave Nadler says of motor gliders: "these are not Toyotas".
It would be so nice to have a self-launch with an engine
engineered by Honda.