Me a logger, not hardly but I do like chainsaws, especially orange ones from Sweden. After workin on stuff for more years than I care to remember, I'm retired now, and just work on what I want to.
I don't know very much about saws at all, just sharing some things I've picked up on with the ones I've rebuilt.
You were asking about removing the crank seal and after it's removed, this measurement is lost. I've never looked inside a 394. Is the seal flush with the case or is it pressed in some?
You do not have to have the factory tool, but you do need to know the installed depth of the seal in your saw now, so the new one can be put back close to the same spot. Here is a PDF of their service tools.
http://www.husqvarna.com/ddoc/HUSI/HUSI2000_AAaa/HUSI2000_AAaa_I0000081_.pdf
According to this, they offer a tool just for installing this seal on a 288/294 which I do not have, but I do have a 288 bearing install tool which has the seal install tool made on it. Without having everything in front of me I can't say for sure it will work but from what I gather from the PDF, it just might.