We have a leak in a roof valley of our new old house. I know it is because there is no flashing in the valley under the shingles. The shingles are cut to end right in the valley and then the valley was just tarred. The tar is deteriorating and letting leaks in. We will be doing a complete tear off next summer and putting the proper flashing in, but I can't let this leak go until then. Any temporary solutions? Should I just re-tar in the valley? Can I put flashing on top of the shingles? How would I attach it? I know this would look terrible, but I need to do something ASAP. Thanks for any suggestions.