I think the broken off ground is quite common. Although there are two straps you don't need both, electrically speaking, in fact the car will run without either because the plugs and other engine attached electrical devices requiring grounds will return through the starter ground. I think the straps are just an additional ground current route. My 740 has had one broken strap for years without consequence.

BillB 89 740GLE wagon 172k (used to have 245GLE, the 2nd best car I've ever owned)