You gotta be really wanting that bike to read the whole listing. On the plus side, put your phone number at the end, if anyone reads far enough to get it and call you, they are probably going to buy the bike.
You've got at least 6 weeks before people start shopping. Use it to put the original fairing on the bike. If it's unused, it will make the bike a lot easier to sell. Sell the Pichler fairing separately, if it's complete you could get a lot more for it than if it's on the bike. Detail the bike well, put Mother's Back-to-Black on the black stuff, especially the cases, to make it pop. Fix the tank leak and then forget about it. Sell the bike as a ready to hop on and go to the West coast from your driveway touring bike.
Just say the bike has been well maintained and have a printed list of the stuff that was done to show a buyer in person. Print up a list of the new parts you have with their list prices(you can get them from MaxBMW). List the used parts with prices 1/3 of list. As far as your ad, just say that you have a large inventory of parts.
Wait until you have someone to see the bike to get into details. Stress that the bike will reliably run at least 150,000 miles and that through forums like Motobrick.com and the K100 forum there is a very deep pool of information and support for these incredible machines. Point out how easy it is to do the routines maintenance so that the owner doesn't need to spend megabucks at the dealer. Mention that outside of tires, annual maintenance cost is under $100 for up to 8,000 miles of riding. These bikes are at the crossover point of technology(fuel injection, electronic ignition) and serviceability. There is no need for the dealer's computers to service this bike.
As far as the speedometer, check that the sensor is bottomed out in the final drive and that the screw holding it is snug. Just the other day a loose sensor caused intermittent speedometer readings on my bike. Took 5 minutes to tighten up the sensor. Also, check that the connector on the right side under the battery cover is tight.
Take lots photos. They sell the bike. Take them from a low angle while kneeling on the ground, the camera shouldn't be higher than 3 feet(2 feet is better). Stay back at least 10-12 feet and zoom to fill the frame. That's how all the ad and magazine shots are taken. Watch out for junky, cluttered, distracting backgrounds(get it the hell out of the garage), a white garage door makes a good background, take your photos on a cloudy day to get the best detail and minimize shadows and glare. Spend some time cropping them. Increase the color saturation slightly as well as the contrast("Clarity" on windows 10 photo editor). If using your phone instead of a camera, hold it horizontally not vertical. Pictures are worth thousands of words.
Here's what I'm talking about:
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