It might be the seal, but it is not something that should require frequent replacing.
Basically, the group of the Silvia seems to leak like this when:
Too much coffee in the basket (IE: over the circlip line).
Crud around the grouphead.
Crud in the shower screen.
Seal is shot.
How old is your Silvia?
What is your cleaning regimen?
Do you backflush?
When was your last clean and how thorough was it?
Do you have a grouphead brush?
Try doing a very thorough clean (see if you can check the state of the seal when you have the shower screen off ) before going down the path of changing the seal.
If it IS the seal, you will need to get your hands on a replacement (check with a sponsor or evilbay), AND instructions on how to do the replacement without hurting anything.
Hope thgat helps.