I've always just tapped the seal in gently with a hammer; never used any other tool. Just tap around the ouside edge, keeping the seal even.
After 40 or so years of using a screwdriver for removal, I finally got a seal puller. D'oh!
Why we get so soon old & so late smart?

I'm actually doing my first timing belt and front seal job on one of my 240's. Prior to this I used to commute 70 miles a day and never had the time or desire to do it myself. I have a set of mega sized metric sockets from HF that has a size that fits both the cam/aux and crank seals. So far I've done just the aux shaft. This seal I tapped in, for the other 2 I may use a bolt like the Volvo special tools to make the installation of the seal as straight as possible. One thing I learned is that you have to be very carefull putting the seal over the shaft or the spring can pop out of the groove. Was surprised not to find any post mentioning that. I had allready done the crank seal with a ST seal and pulled it out has I hadn't know about the spring issue yet and wasn't sure if the spring was still in place. I deceided to use genuine Volvo seals. Seals came out easy enough with a screw driver but I may end up getting one of the special seal removal tools for the next time. Pulled an orange Elring cam seal out of a spare head to verify what the front looked like. Was confused by the oil drain path. Funny thing with that Elring seal practically fell out. My tensioner was noisy so that's getting replace.