Valve stem guide cracked... What now?

[AlexTatar]

I have been changing the valve stem seals on my CLK 270 CDI today, after taking off all the valve stems seals I realised one of the guides have cracked! I've put one of the old stem seals back on to see if it would seal the gap which it does by a few millimetres, however I think under pressure it will start to let oil in. So what do I do now? - Alex