I don't know about the Air Venturi but I had an air leak soon after I bought my Gamo Urban.
I bought some silicone grease, silicone oil and an assortment of metric o-rings for cheap from amazon
My leaker was a usual suspect o-ring or my rifle as explained on youtube . You may need some soap to see where yours is leaking unless someone on youtube can point to a suspect..
Keep it clean and lubed for re-assembly and it'll be fine. There's not much to taking mine apart, I expect you'll find the same.
Last edited by colodog; 01/26/24. Reason: spelling