Automatic MEGANE MEGANE CASE

I have an automatic megane renaut of 2002 that the gearbox fails, when we accelerate so that the revolutionary car turns on the failure light and does not change. ETOs we turn off the engine we turn on again and work again. We have been told that we must change the gearbox, but the repair is very expensive, I have read in a forum that can be due to an grease electrovalve of the box, can anyone guide me?

If it can be removed but anyway to change the electrovalve you will have to lower the box, there are very few that bring external components and this is in very strange cases.