I just changed mine out on my 0-360-a1d on the Viggen. I made the tool that Gene describes and it does work well if you understand the handle can break if you are pulling too hard on the handle. I was able to pull at the base of the handle and pull and pull the seal over the flange.
From my experience is to make sure to clean the seal and bore surfaces really well. Make sure when you are applying the sealer do not get it into the oil return.
Here is link to the lycoming service instructions
I placed a plastic bag over crankshaft flange and applied a thin film of oil to the bag to make it slippery. I placed the new seal in hot water for a few minutes to soften the seal. The bag will make it easier slide the heated seal over the flange and keep oil out of bore. The seal will get snagged on the protutions where the prop bolts go be prepared to see they clear. Follow the instructions in the link and you should be good to go.
Note: when you remove the bag make sure you clean all the oil when removing the bag. You may also want to the apply sealant to crankcase bore before siding the seal over the crank flange. It will be harder to apply the sealant in the bore with the seal in the way. Done right, the bag will help keep oil out crankcase seal bore when sliding the seal over the flange.
Before you install the seal.
1. make sure the spring is removed
2. Make sure the seal orientation is correct before sliding it over the flange.
3. Don’t forget to install the spring.
4. Be careful not to crush or damage the spring if you using pliers or hemostats to install.