Final drive drain plug D15 series 1

True, but the final dives are usually a lot higher than anything else. If you're snagging the drain plug for a final drive, you're likely well past the point of snagging the oil drain plug, hydraulic plug (depending on model), and buried up to your axles. And the final drives are usually pretty well protected inside the rims. My understanding of why they didn't put a drain plug in was that they intended owners to drop them and clean out all the sludge/junk. Which makes sense, and I agree with the principal, but unfortunately many folks just didn't bother because it was too much trouble. Although I know two wrongs don't make a right, I'd still rather have one with a drain plug that someone's changed and monitored regularly (even if they never dropped it and cleaned it thoroughly) than one that's never been changed because the previous owner didn't want to go to the trouble of dropping/cleaning/making gaskets. On my later Allis's that I use often, I change the oil every other year, and do a full drop/clean about every 5 years.