Seal failure means you don't have to worry about debris, but since you will probably not flush the system, then you don't really know how much oil is left in the system. You will need to put at least as much oil back in as you are able to drain out of the old compressor, which will probably be next to nothing.

You should replace the filter drier, so drill a hole in the bottom and see how much oil you drain out of that. The total of the oil drained from both of these old components will give you an idea how much to put back in to make up for it. If it was oily around the shaft seal leak then you lost some additional oil as the refrigerant was leaking out.

So, if you were to find 2 oz. in the reciever drier and an ounce in the old compressor and a dry seal area, then put back in 3 oz. If the seal area is oily add an ounce or so to what you drain out of the old components.

Don't think that you can just pour in a bunch of oil and be okay, too much oil might be worse than not enough. Steve Brotherton said it best, "not enough oil wears out compressors, too much oil destroys them."

The only way to know for sure that you have the right amount is to flush the entire system and then put in the specified amount.

Sorry for the complexity.

All that said, the other important points are: r/d replacement and thorough evacuation.

Good luck,