The October letter did not specifically address whether or not oral sex was or was not considered an unnatural, impure, or unholy practice, and was also not read over the pulpit for general church members leaving many without clear answers.
It did, however, imply that it's not the business of the church what a couple does in their bedroom, and that if there is something they're not sure about, the probably shouldn't do it.
(I'd like to add my own two cents, that decisions like this should always be accompanied with an ongoing conversation involving both partners, and anyone is entitled to change their mind at any time what they are or are not comfortable with.)
There has never been a letter, talk, or statement reaffirming the statement that oral sex is off limits to couples since the original letter in January 1982.
More recently, in May of 2007, the church released a press release addressing how church members and the rest of the world can determine what is church doctrine, and what is not.
Not every statement made by a Church leader, past or present, necessarily constitutes doctrine. A single statement made by a single leader on a single occasion often represents a personal, though well-considered, opinion, but is not meant to be officially binding for the whole Church. With divine inspiration, the First Presidency (the prophet and his two counselors) and the Quorum of the Twelve Apostles (the second-highest governing body of the Church) counsel together to establish doctrine that is consistently proclaimed in official Church publications. This doctrine resides in the four “standard works” of scripture (the Holy Bible, the Book of Mormon, the Doctrine and Covenants and the Pearl of Great Price), official declarations and proclamations, and the Articles of Faith. Isolated statements are often taken out of context, leaving their original meaning distorted.
The Science
We are unique in our gospel in that our doctrine reinforces the idea that sex is a deeply important, sacred, and enriching aspect of our human experience. It's a gift from God meant to unify couples spiritually, emotionally, and physically. It's the means through which we bring souls to earth and create our families.
In order for sex to fulfill its purpose of uniting couples, it needs to be an enjoyable experience for both partners. If sex is painful, uncomfortable, non-consensual, or one-sided, couples miss out on the oxytocin and dopamine rush that creates the deep, lasting and connecting emotional marriage bonds.
It's up to you to communicate with your partner and cultivate a rich and fulfilling sexual relationship. It's up to you to decide what works for you and what doesn't, what enhances your relationship, and what detracts from it.
One of the most fundamental facts that every couple should know (but few are actually taught) is that the research shows that only a small percentage of women (around 20%) can experience an orgasm through vaginal intercourse alone. Most women rely on clitoral stimulation to enhance their sexual experience, and many need it to orgasm. (Where that stimulation comes from is up to you.)
Resources
If you want to learn more about how to cultivate a vibrant and mutually fulfilling sexual relationship, here are some resources:
This episode of "Ask A Mormon Sex Therapist" with Jennifer Finlayson-Fife