Check, check and check again the mainspars, especially the port one for intergranular corrosion. It's hard to spot in it's initial stages but takes root rapidly. A new spar will be required.
There have been a rash of these cases recently. It is apparently caused by a bad batch of heat treatment done all those years ago.
If you aren't already in the PFA, you'll need to be to operate a Permit aircraft. Join now and get the mags etc which make an interesting read and usually have Luscombe's for sale. Try their website pfa.org.uk