So, its my fault that the gaskets, bearings & valves goes wrong.
That means you could not fly that day, you need to go home, regroup & try again.
In electrics I need to maintain them? In what way? In gassers I need to do what? Change the spark pug?
Please give me some light here
Gaskets, bearings and valve failure could easily be from excessive heat. Bearing failure can be from using fuel that has been open and has absorbed a fair amount of water, then raw fuel left in the engine can rust the bearings. Rust particles are very abrasive and will destroy an engine in no time. You mentioned leaking fuel lines and tanks, if these items are correctly assembled and maintained they don't leak. Leaking fuel system means a lean running engine.
OK Gassers, an additional battery to keep charged, most use tygon fuel tubing and it tends to get hard and inflexible after a year or so. Gassers are more vibration so one needs to deal with muffler bolts working loose. The gasser carbs have a few moving parts and gaskets that will dry out if not used on a regular basis especially if you live in a location that adds ethanol to the gas.
Electrics may seem plug and play but they really are not. Batteries have to be taken care of. If you over amp them in flight or don't have propper cooling you can easily damage them. Run too big a prop and you can pulll too many amps from the speed control and fry it. Sometimes you need to program the speed control to the motor. Things like braking, soft or hard start, timing all come into play.
The point i'm trying to make is no matter what power system you use you will need to learn it's requirements and work within them to be successful.