Poorly shaped or fitted wing stays can cause much damage, metal rubbing, cracking or worse..
There are two watchpoints. The first is to isolate the steel of the stay and the steel of its holding bolt from the alloy wing. The rubbing and the common grounding of the side light though the holding bolt to the wing is a recipe for an electrolytic reaction between the steel and the aluminum.
Secondly, as stressed to me by Bill Beck (the Morgan Service Head and Chief Designer for many years), the stay must be shaped to rise up to the bolt and immediately curve down. This simple rule solves most issues. If it not thusly shaped and the stay runs along the underside of the wing, it will crack, rub, corrode the wing or crack the stay. The forces working on the stay (the front suspension, wheel movement and wing weight) must be dissipated. This shape allows for movement WITHOUT damage, all other methods cause harm.
Sadly, the Factory slotted the stays' bolt holes a few years ago to save time fitting them to each car with a one-stay-fits-all. The slots allows the stays to shift, and wing/stay damage became epidemic (made worse when they tried to stop it with a plate extending from the hole atop). I went years with no stay problems and then, when my car returned from the Factory in 2003, my new stays cracked five times in two years before I diagnosed the issue with the slots. I switched them for unslotted stays and haven't had an issue since.
With a strong arm, a big hammer, a drill and a table vice, stays are not difficult to make and/or shape. Those with the newer slotted stays would be wise to switch to made-to-measure stays like the older cars and the rest would be prudent to make sure their stays are shaped like the diagram below. 1. The stay must be flat where the lower bolt is fitted. 2. The stay must rise up to the upper bolt and touch only the wing only at D after which it stay must immediately curve down (C). (3). Place a 1/4" thick rubber washer between the stay and the wing (A). 4. Coat the bolt with silicone to prevent steel and alloy contact. (One can also use a plastic sleeve over the bolt.)
However, better quality products are available. For two decades, John Worrall at Heart of England Morgans has offered these plinths (for both front and back) in high quality mirror polished stainless. He also offers spot/fog lamp bases for those of us who wish to have them fixed to the wing rather than hanging on bumpers or badge bars. Melvyn Rutter also offers chrome-plated bronze plinths for the rear for many years. The softer metal and chrome is more delicate but very pretty as well. I have used them both.
Recently, the Factory has tried to copy them and offers
a similar though less well made product (rear only).