GSDs aren't prone to health problems, they are prone to bad breeders, because the breed is so popular.
A well bred GSD is unlikely to experience significant health problems during his working life because his parents, grandparents and great grandparents will have certificates on things like hips, elbows, thyroid, CERF, etc. GSDs are meant to be very versatile working dogs who can go out in the fields and literally trot all day long, day after day, without breaking down. A dog with health problems is no good to a herdsman or the police.
My future pup's breeder does the following health clearances on all her stock:
OFA: hips, elbows, DM, cardiac, patellas
CERF
She doesn't do thyroid, but I do, so I'll have that done on my pup as well. I've never done patellas, but I suppose I'll start now. I don't think you can have too many clearances and if this breeder is seeing patella problems within the breed and intentionally selecting against it, then it's something I want to select against too. I didn't know there was screening now for DM (degenerative myelitis) and think that is an awesome clearance to have for a GSD.
People talk about mixed breed vigor, but they overlook the fact that 75% of shelter dogs will fail an OFA screening for hip dysplasia, whereas only 20% of well bred GSDs do. That 20% is about typical across the board for large breed dogs. Cole scored in the top 3% nationwide in hip structure. He's never had a lick of trouble from them, but he does have spondylosis (a type of arthritis in the spine), which his breeder did disclose was present in her bloodline. That's why he takes Dasaquin.
There are no supplements necessary if the dog is fed a high quality, balanced diet. After about age 10 I could see the Dasaquin making a difference for Cole but before then none of them seem to notice at all. I do give Dasaquin as a sort of preventive to my other dogs because I know spondylosis is in their gene pool. Dasaquin is a glucosamine supplement often given to dogs with hip dysplasia, but it can be used for any join issue.
Do not feed from elevated food bowls. The research on bloat is split 50/50 on whether elevated feeding is good or can actually increase the risk of bloat. They are designed to eat on the ground, so that's where my dogs eat. A tendency to bloat is largely genetic. A good breeder will know the tendency within her own bloodline and will be selecting against it. Cole's breeder hasn't seen bloat in her line in over 40 years.
Other factors in bloat are common sense things like not working the dog on a full stomach and not giving the dog a full feed when hot from work. So you feed your dog and let him hang around the house for an hour to digest before you do any serious work (or play) and when you return from work (or play), you have a chill down period of about an hour before any meals.
You also don't let your dog gulp a large quantity of water when hot. You let him lap about 15 seconds, then make him take a break for 5 minutes. Then 15 seconds of drinking (if he's still thirsty) and rest for 5 minutes. Just repeat until he's not thirsty any more. If he's not hot, I just let him drink whatever he wants whenever he wants.
What shepherds do need is a solid exercise plan. They need vigorous exercise every single day, rain or shine. They need more than just walks. They need something to make them run. They also need mental stimulation every single day because when they get bored, they get destructive or become escape artists.
A genetically sound GSD feed a high quality diet, exercised properly and given sufficient mental stimulation is unlikely to experience break down except due to injury.