The endcap looks good. It has a female groove for the "o" ring to seat in. I have a feeling that the previous owner had the problem and took it someplace for repair. It had some kind of silicone sealant on it. The guys at the shop tried different "O" rings and a different oil filter. The last try was with an OEM filter that included the "O" ring. I'm wondering if the bolts on the endcap should be torqued.
Thanks for ypur response.