Lost of Manifold Pressure on 914

Hi everybody, I have a Rotax 914, 265 hs.

I bought the plane 2 months ago and flew 15 hours. In takeoffs at sea level with full power was 40 in MP.

In the last 15 days I have only managed 36 in MP.

After it , I was checking the engine and I noticed that my wastegate was not moving. After lubrication I managed to get the wastegate back to work, but keep the same 36 in. MP.

Could someone help me with what I should do?

Thanks