My vinyl roof has some small tears - about 1cm- along the piping at the door. This is where the roof folds. Can these be repaired without replacing entire hood? If not, how long can I expect them to hang in there before I need a new hood
Cheers
The splits are occurring because the vinyl has shrunk. You can “repair” them with judicious use of black silicone sealant to fill in the crack. The hood may have 18-24 months left in it before things become desperate.
If they are now 1cm then I think the time given is wildly optimistic
Given the life of a hood I would change it asap, then you will have a nice watertight hood all the time you own the car.
as long as it takes to start raining in I reckon
Unless of course you Barney Bodget and get a totally dry interior 
http://mx5oc.co.uk/forum/default.aspx?g=posts&t=69217
If the tears are confined to the piping ong; 18 months is a realistic time with the factory hood, aftermarket hoods might be much less. If the actual main part of the hood is ripping, yes, not long to go.
Realistically, expect an aftermarket vinyl hood to last no longer than 5-6 years, less than the service life of the original factory hood.
How long would a Mohair hood last?
I also have a couple of these cracks. One on the drivers side and three on the passenger. The rest of the roof is like new and I cant see for the life of me how it’s going to wear out so quickly. If it’s treated 3 times a year and the cracks are rubbed with black shoe polish (as I have done) then it should last a lot longer I would have thought,?.
Well I like your positive thoughts, I’m hoping too. Thinking about trying black silicone to try and stop it progressing