Just a follow-up was successful removing plug.Soaked several times with penetrating oil,tapped plug carefully with small punch,and finally plug loosened and backed out threads look ok.Thanks for all the helpful info.
Contact the manufacturer I thinks it's Marine Tech.My last boat had swim platform and my ez-steer would not operate without binding I contacted manufacturer and they were very helpful they had a special bracket for my outdrive that solved the problem
Had engine in for winterizing decided to have plugs changed motor ran great all year,merc 135 optimax
mechanic said 1 plug was seized and didn't want to cause any damage so left it in.pesonally I don't think he wanted to spend time
was very busy.What if any problems can I expect in Spring.