It's not all that hard. I've done the front seal on the junkyard 10P15C currently in my '87 diesel wagon. Here's a link to a how-to article: http://www.pelicanparts.com/techarticles/911_Nippondenso_rebuild/911_Nippondenso_rebuild.htm
The subject car is a Porsche, but it uses a Nippondenso 10P15c. I believe the shaft seal is identical between a 10P15C and 10P17C.
The only special tools required are snap ring pliers. As I recall you will need two different sizes. I just purchased an inexpensive package of four at my local auto store for about ten bucks.
It's not that hard a job - I pulled the compressor, replaced the shaft seal, reinstalled, vacuumed, and charged - all after work one evening. You're in for a bit more work - I didn't replace the case o-rings. Don't forget the four o-rings which seal the manifold to the compressor body. I've had these fail - they are exposed to the most extreme heat and pressure in the a/c system.
Oh, and don't forget to reset the clutch air gap when reassembling. You may want to purchase a kit of shims as well. I'm fortunate to have a really good local a/c supplier where I purchased both the front seal and shim kit for ~$25.