For what its worth I will pass this info along. I got it from a friend of mine who used to be the head warranty mgr. for OMC International (commercial division outboards) for South America, Bahamas and Bermuda. He flew all over the place inspecting engines for 10 yrs...and is a BSME, PE and MBA. This is dated back to mid 90s just before OMC tanked. OMC only used 100:1 mix for a couple of years and went back to 50:1 because of corrosion problems. They found that people who let their engines sit for months between use were the ones having warranty work. 100:1 doesn't leave enough film on the internal parts to protect long storage. A 100:1 engine is identical to a 50:1 engine. A typical 80s/90s vintage OMC (evinrude/johnson) only needs 150:1 lube at full throttle and 300:1 at idle. There is a huge safety factor in the mfg. specs. He also said it didn't mater which brand you used as long as it was TWC rated. Concerning synthetic...there was no detection of better wear but was cleaner running...so you can go longer between decarbs. He said synthetic was not cost effective for the avg. boater but to use it if racing because it will turn faster. Synthetic does not cling well to internal parts so fogging is suggested for long term storage in humid climates. Here in Florida that means 2 months. Bill