Here's another unhappy customer with both 518 and 1184 on plastic. The pic below is a Husky 450 that is apart for the 3rd time in 2 weeks. It developes an air leak, wont idle down and races. The cylinder does not have an aluminum crankcase cover that bolts to the cylinder bottom. The cylinder sits directly on the plastic case. Note that Huskie now uses the small rubber gaskets(pictured on the notepad) . The first time this saw was rebuilt, I re-used the old gaskets and supplemented with 518. Air leak, so I took it apart and there was no evidence of 518 on the plastic. Repeat the above and used 1184...same result. Its now apart again and I have ordered new OEM rubber gaskets ($7/ea). When this saw is fixed, it going to spend Xmas under someones elses tree.
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I have several 350s that do not have a problem sealed w/ 1184 but the bases are flat by sanding on sheet glass and 400 grit paper.