The spindle is grease and will not leak but the gear case is oil and has a seal between the top of the spindle and the gear case. Often the oil seal will leak and let the oil splash on the grease washing out the grease and in the long long run letting the oil level get low and then the spindle bearings will be dry.

You can tilt the head and mill but if you see oil dripping out of the spindle later on you will want to drop out the quill cartage and add some fresh grease to the spindle.

If you have never added fresh grease you should do that anyhow. For the lower bearing you can just lower the quill and add it in the slot in the quill but the top bearing must be accesses by dropping the quill.

The quill feed to to be removed by removing the quill spring which is a bit dangerous. The quill is retained by TWO set screws on the left side of the head.