I like my Tassimo but after using it for about a year I discovered that the rubber on the piercing unit wore out and eventually came off completely. This rubber seals the t-disk to the piercing unit so without it the coffee maker is almost useless because it makes a huge mess. I found that replacing the original rubber with rubber “o” rings from the hardware store saves having to buy a new piercing unit, that has to be ordered online for $10.00 + $8.95 shipping. That's $18.95! Hello Tassimo, I could buy a new Mr. coffee pot for that price..... Anyway, here's my fix, I hope this is helpful. BTW, this is my first instructable.

Step 1: Remove Piercing Unit

This part is explained in the cleaning instructions and also can be found easily online so I'm not going to go into great detail about this. Basically, if you've had this coffee pot long enough to wair out the rubber parts and never taken out the piercing unit for cleaning; then I salute you.

Step 2: Buy "o" Rings

Just go to any hardware store and get some new "o" rings. I went to ACE and got one #78 0-ring (stk no. 35715B) which is 7/16 x 1/4 x 3/32. And the other one is a #8 o-ring (stk no. 35725B) which is 9/16 x 3/8 x 3/32. These cost me 75 cents each. And I had a key made.. but I have to take that back because it doesn't work. :(
All I did was match up the rings they have there with the piercing unit that I brought into the store. Maybe you can find a better match.

Step 3: Put It in Place.

I put the "O" rings on the piercing unit then placed it in the machine but you could put them on with the piercing unit in place. One thing to watch out for is when you take the piercing unit off the machine keep your finger over the "O" rings or they may fly off into the back part of the coffee maker. That happened to me and I had to tip over the entire coffee maker and shake it out.