How can I remove and replace a Bosch WFF1201 door gasket?

The rubber seal that rests against the glass door is broken about 1in is missing, hence water is escaping unto the floor. What is neccessary to replace this myself should I order a replacment Door gasket. If however this means removing the drum or a major undertaking, how can I get a qualified repair man in my area Ramsgate, Kent. CT11 LZ0