Spark plug color

If the," ... previous owner had some kind of lube on threads", and the Lube was a White Color;  that was the correct Lube and was applied by Rotax at the factory when first assembled.
It is Not there for Lubrication, it is Heat Sink Thermal Paste, used to keep the plug temperatures under control.

Adding EGT sensors would be a good move.
Adding O2 Sensors, Not so much.
Any residual 100LL in your fuel tanks will destroy the O2 sensors.
O2 Sensors and Lead to not mix.

Otherwise, your Plugs look normal for 80+ hours.