should I quit my job of 25 years ?

Let me sum it up , Been there 25 years , good pay and good benefits but terrible management and a very vindictive manager. He passed up some of us older technicians for promotion and promoted a non-union member and didnt even post the job for us to know about it ! I have dreamed of leaving but I can retire in 5 years and I am at the top of the Seniority list . I have a new job lined up in the same field. Should I tough it out or take a chance somewhere else ? This is a tough decision. I do not know what to do ! I dont like going to work and I dont even like my co-workers anymore. But I am in familiar turf. Would you change to a new job at 50 years old under these circumstances ?? Thanks