Forgive me, but I've never been able to understand a mechanism by which lubrication would be present for us, short of the sigmoid-colon procedure (which seems to over-lubricate). Our vaginas are designed to aesthetically resemble CIS female vaginas, and they do that remarkably well. However, since they are unavoidably rearranged CIS-male parts, certain undeniably physiological differences cannot be ignored:
1) Urethral tissue: in my "other life" shall we say politely, pre-SRS, I got no lubrication from my urethra. What came out was prostate fluid/pre-ejaculate. The prostate shrinks after HRT. Cowper's glands remain as well, but they contribute only a small percentage to pre-ejaculate material in CIS males, and even this comes out of the urethra. They are not modified or re-placed elsewhere to offer lubrication after SRS. If I recall right, there wasn't even any ejaculate left after 6 months of HRT. Any lubrication post SRS is emerging from the urethra, but not from the lining of the urethra...why would it? Does the urethra lubricate in CIS females? No. That's the job of the vaginal mucosa. Does it lubricate in CIS males? Again, no. That's the job of the Cowper's glands.
2) Scrotal tissue: a number of studies have been done that show neither the penile inversion nor the scrotal full or half thickness grafts turn into mucosal tissue of the kind that lines CIS vaginal canals. They are not stem cells; they cannot shift their function any more than any other cell. Indeed, they don't even "know" they've been shifted internally. I was on HRT for two or three years before SRS... I never noticed my scrotal or penile skin lubricating itself while aroused due to estrogen 'changing' anything. Why should it start just because it's been sewn into a canal internally?
3) Clitoral sensitivity: physiologically, although they have the same function, the clitoris under microscope shows a nerve density far higher than the glans of the penis. Meaning, a small chunk of glans used to make a clitoris might look like a clitoris, but cannot possibly have the same sensitivity. From experience, I know this to be true.
This doesn't discount the positive aspects of mentally feeling correct and getting just as much or even more pleasure from sex or orgasm post SRS. But I do question surgeons that promise all sorts of stuff that don't seem possible to deliver. Dr Suporn did mine, and he was quite clear that lubrication was not something to expect. He was right.