When you say they used "vegetable oils", do you mean they used a vegetable oil bought from the grocery store, or that they used one of the blended biodegradable oils specifically made for chainsaws?

I've used both the Stihl Bioplus (https://www.stihlusa.com/products/oils--lubricants-and-fuels...) and Husqvarna XGuard (https://www.baileysonline.com/husqvarna-x-guard-bar-chain-oi...) for a couple years now, and have no complaints other than the price. I do occasionally switch to back to mineral oil when I run out, so perhaps this has helped me to avoid problems.