There's more than likely a blockage somewhere, or even a hole worn in the pipe on your oiler.
Chain oilers once tuned in properly are the best way of lubing your chain, but its by no means the only attention a chain needs. C'mon, were not that thick!
Scottoilers do only oil one side of the chain, but capillary action moves the oil to the internal parts of the links. It won't necessarily oil the outside of the links to prevent rust.
One thing it will do is pretty much double your chain life, and massively reduce the need to adjust the chain slack.
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