WD-40 is a degreaser, which could remove remove lubricant and dry out the garage door springs. This can cause unnecessary friction in the springs and lead to early failure. While WD-40 has many valuable applications, it is not recommended to use it on your garage door's springs.
A repair may just reveal more issues after it's working. If you plan to stay in the home for a while and the opener is over 5 years old, it may be a great time to replace it. The quality of the existing opener should also be taken into consideration.