If you have a '69 912 you more than likely have a 902/16 or 902/06 transmission with A,GA,O,U,Z gears and a 6:29 R/P. You also have a magnesium case which is a lot lighter than the 901 transmissions. When you do the math a 902/16 comes out geared about the same but slightly shorter than a 902/1 or 901/02...You won't know until you tear it down how many syncro's and dog teeth you'll need but it's safe to say probably most of them except fifth gear which doesn't get as much wear as the rest...The 1st/Reverse slider is expensive but probably needed if your having issues with 1st gear. You cannot replace 1st or 2nd gears. They are a permanent part of the input shaft. If your 6:29 R/P is in bad shape I would highly recommend going to a 7:31 R/P to both take advantage of your current gear ratio's and the stronger R/P. Your gearbox is geared lower with the 6:29 and the 7:31 will make your transaxle way better on our lower profile tires. You can pick up a fourth and fifth gear from a 914 transaxle pretty cheap and Dr. Evil a.k.a. Mike Lesinak most likely has some he can sell you far cheaper than getting them on ebay or what have you. I rebuilt my first transaxle using his video and had no problems doing so. With that said you do need the special tools he makes to do so. These he can also sell you pretty cheaply. I'd email him and see if you can get a hold of his video on CD. Also, he can do your transaxle for you for around $300 plus parts and shipping. I shipped him my 902/16 so he could set the pinion depth on it with a 7:31 R/P. I LOVE my custom transaxle. it has A, GA, O, V, ZD gears and makes it much nicer on the highway and I'm geared taller than the average autocrosser who has an F gear.
Dr. Evil a.k.a. Mike Lesinak
mike95125@yahoo.com
Jamie