There is no doubt that the mobula7 as reviewed here is an excellent quadcopter that has redefined what ducted micros can achieve at a fair price but the key flaw in this model (and other ducted quads) is lack of durability in the frame. Frames for the Mobula are not expensive at $4 here but waiting on a frame to be delivered represents downtime.
Welder's glue is often recommended but is not available everywhere and shipping can be precarious on this. I tried the E6000 glue from banggood on a whim and am really please to report it works perfectly, is inexpensive and being available from Banggood, is available worldwide. It comes 15ml, 50ml and 110ml tubes for $3, $4 and $7 repsectively at time of writing. 15ml is plenty for the small amount we need for repairs. It also has a very fine metal nozzle which is just perfect for the fine work we do on repairs. The cap has an integrated pin that sits inside the nozzle for storage so never blocks.
The glue itself is a clear viscous liquid and dries clear. Instructrions suggest to use it as a contact adhesive on smooth surfaces but this glue is so versatile it will move into cracks. It sets semi-hard with the flexibility we need for these flexible plastic frames. For example superglue in this application is no good because it is too stiff and brittle as a result.
Update: after more crashes and more breaks I'm pleased to say the breaks are in different spots to the repaired spots i.e. the glue joint are at least as strong as the frame itself.
I can strongly recommend this glue, it is cheap, easy to apply and most importantly if performs really well for repairing plastic frames and as a general all-purpose glue for quadcopters.
E6000 Glue is available worldwide from Bangood from $3