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If you need a replacement or upgraded oil tank, it's good to know which one is which before you buy one.
1983-2001 oil tanks look very similar when viewing from the front or even side in some cases.
The best way to determine the year model of OEM oil tanks is to look at the rear of the tank.
Looking at the bracing and fitting locations will tell a lot.
There are other details that tell the year model as shown below.

The oil tanks have been upgraded over time to make them stronger at the connection points to their respective battery box.
The weight of the battery is the usual suspect that causes cracks and leaks. Using too much torque on the battery box to tank bolts is another.

Below are the known changes on the rear of oil tanks from 1983-2001.

1983-1993 oil tank:

• Standalone welded bracket on the front that mounts to the battery box.
• Uses the 2-hole battery box with the welded 1/2“ nipple under it.
• 4 oil line fittings
• Single threaded hole on the upper rear to mount the starter relay to the tank.
• Curved rear contour.

1994-1996 oil tank:

• Wider front bracket for mounting the battery box.
  Bracket has arms spot welded to the tank extending to the two front tank to frame rubber mount holes.
• Uses the 3-hole battery box.
• Only has 3 oil line fittings.
• Still has the threaded hole on the upper rear for 83-93 starter relay even though the relay was moved elsewhere in 94.
• Curved rear contour.

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