Is my tranny or differential broke? Options

[HardHead93]

The car has been leaking gear oil. I thought it was an axle seal so I took it to my local shop because they installed the original seal and would warranty it. Come to find out it is not the seal. The axle has some serious in and out play in it. When it moves out gear oil leaks out. The shop has tried 2 other brand new axles and the problem is the same. The last axle would not click and lock in. I have a helical LSD in an S54 transmission and I am running a Gen 4 3sgte tuned for 340 hp on E85. I track the car so it gets beat on pretty hard. The shop is having a hard time getting a good part number because the original part number is discontinued but superseded by another. One axle came from OReilly's and the other came from AutoZone. Is the tranny or the differential broke or am I not getting the right axle? Has anyone else had this problem?

[HardHead93]

I am pretty excited about the gear ratios.

The S54 has the following ratios:
First Gear: 3.285
Second Gear: 1.960
Third Gear: 1.322
Fourth Gear: 1.028
Fifth Gear: 0.820
Reverse Gear: 3.153
Final Drive: 4.176

The S51 has the following ratios:
First Gear: 3.538:1
Second Gear: 1.960:1
Third Gear: 1.250:1
Fourth Gear: 0.945:1
Fifth Gear: 0.731:1
Reverse Gear: 3.153:1
Final Drive: 3.944:1

The S54 at 4000 rpm in 4th gear hits 69 mph while the S51 hits 80 mph. In 5th gear at 3500 rpm the S54 hits 76 mph while the S51 hits 90 mph. This means that the car will not rev high and drone cruising on the highway. Also, the car will have a higher top speed and since it is an aftermarket ECU, there is no governor. The other nice thing about this transmission is the first 2 gears on both transmissions act the same and 3rd gear is a tad bit longer on the S51 so acceleration will not be too affected. The car is riding on 17" x 8" rims with 225/45r17 tires. That makes the tire diameter 25" wide. I used that tire diameter to calculate speed. I used the calculator on this website: http://www.apexgarage.com/tech/gear_ratios.shtml

This post has been edited by HardHead93: May 2, 2019 - 10:04 PM