I nedd iformation on Briggs Vanguard 18 hp engine

I have I 18 hp Vanguard engine. I need to know what the compression should be. I have checked the compression and I show 135 on the left side facing the flywheel and 120 on the right. I have to replace the dip stick tube seal every once in a while and was wanting to know if this could cause this. Could it be building up pressure in the lower end. The engine is also running rough and I am getting oil in the breather. Could this be caused by the breather assembly.

Thank you for your tome.

Melvin1942

I nedd iformation on Briggs Vanguard 18 hp engine