These switches are notorious for failing (and leaking) - the same part is even used on BMW motorcycles, with a similar failure rate and mode.
It's cheap (especially if your can source an aftermarket part - and mostly likely it'll last longer too!) and easy to replace. If your has oil on it, it needs replacing regardless, so just replace it and see if that sorts your leak.
On my BMW Motorcycle, I used a Tridon branded unit after having three "genuine" switches fail on me.... no issues in the 5-6 six years since.