Replaced washer drive block. The drive block has two small grooves (like keyways) that mate with tabs on the drive shaft. When the machine activates the brakes at the end of the spin cycle the inertia of the spinning drum (especially with a heavy load of clothes) causes the grooves in the drive block to strip-out and skip over the tabs on the shaft causing the loud noise.
The repair job is fairly straightforward if you follow the video instructions. The tub wrench (spanner, p/n AP6832671) is essential to remove the retaining nut from the drive block as there is not enough space inside the drum to fit a large channel-lock. It took a few hard hits with the hammer on the wrench to get the nut started off. After replacing the drive block be sure that the drum is fully seated before trying to thread on the retaining nut and agitator bolt. You have to wiggle the drum around a bit until it pops back down into place.
I also replaced the three small and one long suspension springs as a precaution while the machine was apart. They appeared to be OK visually but might have weakened some.
The machine is back to normal, no more loud noises. Son & daughter-in-law are happy campers plus my son learned how to fix the machine in the process! The service from AppliancePros was outstanding. The parts arrived in less than 24hrs (I placed the order at noon and the parts arrived at 11 am the following day). Their instructional videos are excellent!!