If your machine is 3 years old that seat gasket should probably be okay, but if it's hard you'll need a rebuild kit. Stefano does sell them:
http://espressocare.com/Qstore/Qstore.c ... me+OPV+Kit

It's 3 years and 2 months old. The machine is turned on and under water supply pressure (about 35 pounds) 24x7, except for when I descale it. I descale three times a year.

The seat gasket doesn't feel hard to me.

Here is the mushroom and other parts from the gicleur chamber. The brew valve looks pretty beaten up. The gasket has a lot of cracks in it.

Here are the preinfusion chamber parts. This is the first time I've ever taken this off the group head. The valve is broken, which likely explains the constant leak from the bottom of the drain valve.

Drain valve assembly.

Wow! That thing looks years older that actual, at least all the rubberized seals are quite hammered.
Looks like it's time for a full once over on the machine seals. A home barista's work is never done!

I was wondering about that too. I keep it running 24x7, but even so, I was surprised that it could be in such shape after only 38 months. I don't know what what kind of wear I should expect in that amount of time, but I wasn't expecting anything this severe.

As I said, I descale every 17 weeks. I've disassembled and cleaned the mushroom and gicleur chamber three times (once a year). This is the first time I've ever disassembled the preinfusion and drain chambers. There's no telling how long the preinfusion valve has been broken. It was still pulling decent shots, with the only issues being the constant OPV/bypass valve flow under pressure, and the constant dripping at the drain valve. I'm not sure when that started.

I finished a complete group head rebuild, including all valves, gaskets, and springs, and also rebuilt the OPV valve. I don't know that I really needed the latter since I was able to fix the OPV bypass overflow by adjusting the pressure on the Procon rotary pump. Thread here -- Rebuild OPV / Bypass valve

The machine is like new again, very smooth to operate.

I've always left this machine turned on 24x7 in the past. In an effort to extend the life of the valves and gaskets, I'm going to start powering it down overnight, so it's only turned on during the day when I'm likely to want to pull a shot.