ANDREW - Which part exactly did You break? The push button or the rod it threads onto? If You broke the rod You have to make a new one because they and the whole rockshaft assembly are "NLA" last time I checked for one for My 72 about 5-6 yrs ago....72 is the same as a 73 except for some cosmetic details. If You broke just the button, the repair isn't quite as complex but close. The whole rockshaft has to be removed, four bolts, two on each side that support the rear of the foot rests plus the small capscrew on each side that holds the front of the foot rests have to come off, plus the two bolts that hold the quadrant (curved piece with the notches on the bottom) the lift lever rod engages. Once You have the rockshaft out the release rod pushes up and You can remove the remains of the push button. Parts are/were still available when I fixed My 72. The release rod will not come out of the top of the lift handle because of the bend on the bottom and the remains of the button on the top, plus the release rod hits the rockshaft and has to bend to be removed which makes it bind inside the handle and won't work so leave it in the handle if it's O-K. You should replace the spring and there's a special flatwasher or two in there that I would replace also. Good time to replace Your "float Button" on the front of the lift handle if Your's is missing or sticks. Once You have the parts inside the top of the lever the new button simply threads onto the release rod then You can reinstall the rockshaft onto the tractor. If You can get the front capscrews out and back into the frt support of the foot rests let Us all know how You do it. I've tried EVERY combination of socket, u-joint, swivel, & extension I have, every combination wrench known to man and they are tough to get out & back in. You can easily see them, touch them, but defy every tool I own! They're not stuck or too tight, just can't get a wrench on them then be able to turn the wrench!
If the release rod twisted off, I think it's 5/16" round rod, thread one end of a three ft length of rod (5/16" coarse threads)from a hardware store to accept the new top button, slide it into the handle with all the springs & washers required, cut the rod to an approx. length of the old one first before You install the replacement rod, then with a propane torch, MAPP Gas torch, acetylene torch, heat the bottom of the rod to a red hot condition about an inch from it's end, use the old rod for a guide or pattern, and carefully bend it to the correct angle. I took a small piece of tubing that fit over the 5/16" dia. end of the rod to bend it, keeps the end that engages the quadrant straight and makes a sharper bend, Then reinstall.
PAUL - Back when the DOT shop was still standing I used to take My old engine oil to the recycling tank at the garage. That grader was always setting there but I never looked at it too closely. In the last couple months the recycling tank, the whole shop building and most of the hill it all sat on is "GONE!" I hope they rebuild the garage & oil tank, etc. I liked being only about 3 miles away from where they stored the snow plows....Our road was one of the first plowed out every time it snowed.