Re:qingjiao
When expressing the idea 'stopping one's service in the army', I cannot see much difference between the two phrases. But 'to leave the service' has another meaning to stop accepting some kind of service.
I don't know why you must figure out a clear explanation to the possbible difference as you see it. Actually, I myself cannot explain well the difference between 'sort' and 'type'. And I think it is always difficult to explain a language, as language can simly be a habit. Maybe you can know how to really use them by paying special attention in your daily reading or listening.
'at the sight of spiders' means that 'when you saw spiders'. This is to describe a situation.
'the look of spiders' means 'what the spiders look like' or their appearance. so you can see the difference.