1998 Johnson Evinrude "EC" 90, 115 SPL Service Repair Manual, P/N 520209, Page 168Get this manual
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7 Clean and degrease the exhaust housing and adapter mating surfaces with OMC Cleaning SolventApply OMC Gel-Seal I to adapter flange of the outer exhaust housing
10 Apply OMC Nut Lock to threads