Thanks for the above advice Richard.
I played the Mandolin this morning for an hour and the grove that i very carefully re-cut    seems to be holding out? The end of the nut looks a bit like a broken tooth but Im satisfied that the mandolin tunes ok and that the action Brian set up has not been affected by my
workmanship.
Having never attempted such a repair i am quite pleased with me self. I cant do nothing about it until after Knockholt whereby I will go and see brian. I was hoping to get my nice little traveling guitar set up next by Brian but that goes to the back of the queue now the mandolin comes first.
I have only been playing the Mandolin for 8months now and progress is slow but im getting used to the strings and can pick through a number of different scales and the chords are now simple.
There are 3 things about a mandolin I have learned,1) There bloody temperamental.
                                                                                             2) they like to be played every day or                                                                                                                                                                                                 they sulk.
                                                                                             3) They are very highly strung and tend to have break downs without warning Ie like my just did. Bloody parlarva.