My existing vinyl hood uses the original hard plastic rain rail. The rain rail is still in good condition but drips appear from the back of the rain rail where the locating studs pass through. I am about to replace the hood, which is past its best, with a complete mohair hood and frame which comes with the later more flexible rain rail. What can I do to prevent leaks through the stud holes? I am tempted to use some silicone sealant around the base of the studs. What do other owner’s do?
I did exactly as you are thinking of doing. Just a small blob around the base of the stud and push your rail rail on. I had a few splits in the rail too which were sorted with some very strong clear sticky tape, can use duct tape too. No leaks again, that was my Mk1 that had sprung a leak. On replacing the vinyl for a mohair hood on my Mk2 I did as above, again water tight, good job.
Please don’t use silicon sealant, it is not the way forward for rain rail repairs or installation as water can go every which way and if it gets trapped in there its a big problem, if done badly and below is example of a rain rail repair damage done with silicon seal.
When we did the NEC Restoration show, we looked at rain rail repair as a necessity when replacing a hood on the demo car - and what came up as the best repair method was use of and adhesive aluminium tape, easily available in most DIY sheds and has a multitude of uses hot and cold - this can be used to repair over all previous fixing points, it is malleable to shape on to the rail, remains adhesive even when wet and provides a ‘new’ seal when putting the rain rail back on to the bolts.
After learning about that stuff, I’d say I wouldn’t do it any other way now, sorry I didn’t take more pictures to highlight this stuff in action.
One method is by use of foam washers on the studs. Its what Robbins does with their replacement rainrail, and Dr Eunos supplies washers. 
Iain F
Updates on the mazdamenders FB group page on using alloy tape to repair the rain rail if pics are needed buddy, been done for a guide thats being built that will be locked into the main board if needed.
OP …do not ever use sealant, or gaffer,duck tape.
M-m