The clutch plate retaining clip problem means new/rebuilt/replacement tranny time. No real fixing that. Expertly rebuilt valve body is just under $500.
So, had the car been taking a little bit longer than it should have to change gear into reverse? If yes, then it's probably the check valve problem.
Do you know if it snapped/popped when you tried to engage reverse? If yes then it's probably the reverse clutch pack retaining clip broke off the clutch pack.
If you can drop the pan check for chunks of aluminum. If chunks of aluminum are present then the clutch pack body is shot and it's new tranny time.
Had the reverse clutch pack retaining clip break off the clutch pack body in my 5HP30 at 160k or so while still on the original fluid. The retaining clip problem isn't very common at all. The check ball problem is the usual problem which is fixed with a rebuilt valve body.
Don't know about the check ball problem, but with the retaining clip problem it's not a problem to continue to drive it. Due to the nature of the check ball problem I probably wouldn't drive it if that was the issue. Do believe I drove about 900 miles on my 5HP30 after the retaining clip snapped off and I lost reverse. Most of that was driving to the shop to get another tranny slapped in from another M-Sport.
Cosmos Black/Black 1995 540iA M-Sport
BMW Individual Exclusive Edition, 1 of 65 total, 9/25/95 Build