Te magna auto transmission has no drive it came back but has gone again.they told me a new transmission is needed at $4000 but it was fine before i went away and now it just wont move it sat for 15 days

Smell the transmission fluid .. it it smells burned or is dark in color then they may be right about needing a new one .. if not then it could just be clogged .. that frequently happens if the fluid hasnt been changed for a long time then when it is changed (or added to) the new fluid loosens up stuff which can clog the small holes that fluid is directed thru ... if thats the case there is a cleaning method where a solvent is forced thru the transmission and converter .. that should desolve most of the gluck that could be clogging things .. that cleaning costs a little over $100 including new fluid .. it may not work but might be worth the gamble ...you have to either trust the mechanic to do the work or watch them .. there are shops that claim they did the work but dont if no one is watching .. they dont have to take the transmission pan off to do this work ... so the filter doesnt get changed if its inside .. but it does get reverse flushed with the solvent ... that might be ok if the tranny isnt really messed up .. that saves some bucks in labor and parts .. the transmission repair places tell me to expect to overhaul most transmissions between 70,000 and 150,000 miles .. more than that is luck .. transmission rebuilders other than the dealer might have a much better price and warranty .. but call BBB for each potential repair place ... many have bad reputations a few have really good marks and might be worth a few extra bucks .. ..