Union workers at Mercury Marine in Fond du Lac are getting one final chance to keep their jobs. The maker of outboard motors agreed yesterday to a third union vote on proposed contract concessions. It will take place tomorrow night and Friday. If it’s approved, Mercury promises to keep its current plant in Fond du Lac, with 850 jobs. It would also give extra work to a non-union plant in Stillwater Oklahoma, where Fond du Lac’s production appeared to be headed after the union first voted no to the concessions on August 23rd. The new proposal is the same as the old one, but both sides say it clarifies things to make it easier for employees to understand. It basically calls for a pay freeze, higher health premiums, and 30-percent less pay for new workers and those returning from playoffs. The union started a second vote last Saturday night, but the firm said it was not completed in time to meet an earlier deadline to accept the deal. The voting continued Monday anyway, but the union eventually halted it. If the plant stays, Fond du Lac County Executive Alan Buechel says there’s also a good chance that Mercury’s headquarters will stay put in the city. Those headquarters employ another 800-to-900 people.