Been running used oil for decades and never had an issue.
How much is an average OEM bar 40 bucks. How much is the cheapest bar oil on sale 6-7 bucks. How many gallons of the average 10 dollar oil does it take to equal a 40 dollar bar? 4 gallons. I have ran hundreds of gallons of used oil through the same saw with zero issues. At 10 bucks a gallon and 100 gallons of oil equals $1,000 At an average of 40 bucks per bar how many bars can you buy with $1,000 = 25 bars. I figure the risk of running used oil vs buying 25 bars per year puts me ahead by tens of thousands of dollars.
As for slinging the oil off, that does not equate to all the oil used. Most of the oil is dragged off by the saw dust, not slung off by the spinning chain.
If you are worried about dirty oil just use used hydraulic oil. Plenty of that can be had at any heavy equipment service center for free.