Hi, needing some help with a satellite connection dropping out.

Using a dual lnb set up via a 22khz box through to a new decoder.

Im having an issue where the link stays good for a day or two, sometimes more, then suddenly drops out completely - no quality loss, just looses the link.  The strength is always around 92-95%, but the quality is only ever around 70-80%.  I am receiving two signals, one Optus D1, the other is D2, it seems to be the D1 signal that keeps dropping.  The lnb bracket is not perfect so I'm trying to secure that first, but could I be fighting a loosing battle with a failing LNB? or is it more likely to just be the lnb skew/angle?  Just seems wierd to me that it stays for so long and then suddenly dissappears - unfortunately I don't know enough about how the connection works to decide on what would be the most likely issue.

Thanks for any help.