Good deal- R-12 is the way to go... Just flush the system to get rid of the old oil. New o-rings, dryer and expansion valve. Have any leaky hose rebuilt.

Generally, the ceramic seals don't loose much freon. If you have leakage at the front seal- the seal is cracked.
I read the new Denso press-release last week. I think it is a year old.
M