Assuming "oil based lube" means lube specifically DESIGNED FOR SEX, I suggested that he buy some and read the warnings. I don't know anything about oil based lube because I have never used it. I'm not suggesting
anything counter to "everything" ever written about anal sex

If it was wrong of me to suggest he read the package itself, excuse me. I stand corrected.
Nothing in my previous post says that he should use the lube necessarily. I said that I cant see how an oil based lube in her ass would cause an infection in her vagina unless he's using TOO MUCH of the stuff.
At the risk of sounding like an ass,
perhaps you should read my post again a little more closely.
Now, as for the vagina being self-cleaning, you obviously should have done a little research before making the statement that it is not. I suppose my GYN, who has spent more time in school learning about my anatomy than I can imagine, is wrong too.
See articles below:
GayHealth: Private Parts
(The vaginal walls are continually producing secretions necessary to provide lubrication, to cleanse the vagina, and to maintain the proper acidity to prevent infection.
The vagina is a naturally self-cleaning body part, so douching isn’t necessary to keep the vagina clean)
Somazone > Fact Sheets > Sexual Health > Vagina Info
(All girls have discharge from their vagina, which is completely healthy and normal.
The vagina has its own self-cleaning mechanism. The discharge flushes dead cells from the vaginal lining as well as lubricates the vagina.)
If you aren't satisfied, do your own search.