every morning i have problems with the 1st and 2nd speed at the first changes. i need much more power to push the lever if i want to change speed. After 15 minutes everything is working fine. The problem began when a technician spilled valvoline by accident inside the gear disk !!!

Oil was spilled onto the clutch? Does it grind into reverse? If so, I'd worry the clutch disc is ruined. Otherwise perhaps a gear oil change, Redline oil seems to help with this type of problem.

Oil was spilled onto the clutch? Does it grind into reverse? If so, I'd worry the clutch disc is ruined. Otherwise perhaps a gear oil change, Redline oil seems to help with this type of problem.
No it doesn't grind... There is no strange noise when i'm driving...I don't know the redline oil...will it reduse the attrition inside the gearbox...how can i find it in the local market???

The problem began when a technician spilled valvoline by accident inside the gear disk !!!

Make them fix it!

As long as the clutch disk hasn't deteriorated the Redline oil may work. It helps with stiff shifting gearboxes due to wear & age. Not all stores carry it, but you can find it with a Google search. If the clutch disc were going bad from the oil I would expect it to be difficult to get into reverse also.