This job was complicated but not very difficult until it came to loosening the bolts that attached the spider arm to the drum. Follow the video and be prepared for it to take several hours.
In my case, I doused the bolts with penetrating oil and heated them with a hairdryer on high heat (my lame substitute for heat gun, which I didn't have). Got 4 of 6 out with some effort and then the last two -- one each on different arms -- were so tight that I used a 25" breaker bar + bolt extractor socket to get the 5th off. Would HIGHLY recommend this method to begin with if I had to do it again.
The last one stripped so I hacksawed through the head and then pulled it through the hole. It gaped the hole a bit but I was able to tap back in to place with ball peen hammer and smoothed the edges with a file. You can order the custom replacement bolts from APP for $4.33 (http://www.appliancepartspros.com/lg-screw-customized-4000fr4031b-ap5224413.html#ixzz55WD9DM2F) but I didn't want to wait so I replaced it with a Stainless M8 1.25 16mm flat head screw from my local hw store for $0.98. It reached well into the spider arm and provided a secure mount. I also applied Locktite (blue) to the bolts when re-mounting.
I was really surprised how deteriorated the arm was -- it literally broke off in parts when I began to pry it away from the tub-- so I took another poster's recommendation to spray paint the arm before reinstalling. Gave two coats of Rustoleum to help prevent future deterioration. I'm willing to bet that I'm the only LG customer with a high-gloss forest green spider arm!
Took me much longer than expected due to the difficulty with the bolts. I hope to never see the inside of this washer again.