First things first...sending tons of virtual hugs for you and Lenny. Now for the "fun" part. You can do this and it will be far less stressful coming from someone Lenny knows loves him.
If you don't have a grooming table, find a comfy spot for both of you. I put a cozy blanket over the guest bed and tied the leash to the bedpost. Use a muzzle. Follow vet instructions as reviewed above.
My boy "Rock'n Rowdy Rascal of Thor" went through this in 2016. He growled, but had never bitten anyone. The muzzle was a preventative measure. Once it went on, he relented and snuggled up to whoever was treating him. Rascal crossed the bridge in 2017. By the time we got the Cushing and cancer diagnosis he had deteriorated too far for treatment.
You are 2 years in and that lends hope. We are here anytime you need to a shoulder. Your Basenji family in this forum is a treasure of knowledge. They know more than many vets.
@scewbydoo One of our vet techs volunteers with the shelter where she was born. Her mom was labeled as Jack Russell. Her goofy nature makes me think Boxer mix, but who knows. The shelters down in S. TX aren't the most accurate at breed identification. I once had a shelter in San Antonio send me a picture of a brindle Basenji they wanted me to pull...it was a calico cat.
Regardless of breed, Roxy is home.
Your pup is gorgeous. He is what we call a "Beautiful Blend", my vet calls them "Lucky Little Street Dogs" because they look just enough like a purebred something that they are easily adopted. The only way to be for certain of your boy's breeding is to have DNA testing done.
My Roxy looks very similar. She was presented to me as a Basenji, but I knew at first glance that she was not.
The right Basenji has great potential for a special needs child. My Bunmi came to me as a "vicious dog" through BRAT. The facts were that she was defending child. She developed a strong bond with my special needs Bonus Son and my Grandson. Bunmi is nearly 16 now, has several health issues and is blind, but she still dearly loves children. BTW...Bunmi (her original AKC name) is Swahili for Gift from God.
I recommend communicating with reputable breeders and with BRAT www.basenjirescue.org. Not all rescue dogs are damaged, the are often just in the wrong situation.
Have you considered lure coursing? When my pack was young (we have one left-age 15), Hubby would put a white plastic grocery bag (with a light weight so nobody got hurt) on a small fishing pole and pitch it around the yard. They went nuts. Literally played until Hubby couldn't play any longer. All slept very well afterward.
We also took them to a lure coursing center. They loved that too.
My Bunmi has an anatomical problem that prevents her glands from expressing properly and she's suffered two abscesses. I give her organic pumpkin mixed with vanilla yogurt and coconut oil a couple times a week. Sweet potato is a seasonal treat that serves the same purpose. I have no idea if organic has any importance, but it seems to taste better to Bunmi than the regular. Vanilla yogurt serves to keep good bacteria in the gut and make the pumpkin more yummy. If they don't like the coconut oil, you can rub it on their belly (like a moisturizer) and they will lick it off.
Her regular vet advised against anal gland removal unless there were no other options. He explained that if you remove the glands, the dog will likely have issues with bowel incontinence. An occasional leakage of fluid is better than bowel incontinence.