LNB's dont cost much and are relatively easy to replace
http://www.argos.co.uk/static/Produc...%3ESKY+LNB.htm
There is a site that explains the degree of rotation\skew of the LNB on the arm in relation to the dish (dependant on where you are in the UK)
http://www.uk-satellite-tv.co.uk/tec...lp_154117.html
As its an exposed point when you get the signal back to a high enough quality make sure all securing bolts\nuts\screws are tight as strong winds, moisture, hot\cold can cause some movement.
Also & I'm sure if this would work you could cover the LNB and some of the arm with a clear strong food bag and tie-wrap it to to the arm to stop ingress of salt water into the LNB. There should be no degridation of signal received to the LNB.