I cracked the compartment lid and had a peek at the battery terminals; sure enough, this thing was stored with batteries installed and a chemical reaction had taken place.
First item of business is to crack the shell. Removed the two visible screws (the lower one was behind a press fit rubber plug) and felt a screw sized indention behind the product label. In punching through the label to investigate, I can report that indention is a casting mark and can be left alone, there are only two screws on the back half of the shell.
The front & rear halves of the enclosure are snap fit together. Pictured are the three major points: above "LINE" (which is easy as you can slide your finger into the battery compartment and pull that one right out, I saved it for last), above "USB" and at the halfway point of the bottom silver case halves. Once the bottom was freed, the USB connection followed, allowing me to ease the LINE connect open from the battery compartment. Other side is similar, but only one side needs to be unlocked to separate the case halves.
The corrosion here effectively insulated the battery stack, rendering the unit inoperable. I believe the foam blocks are there to prohibit side to side movement of the contact spring, and are therefore important to retain.
Removal of the contact is easy: pliers on the elbow at the base of the spring will allow you to pull this part out when the solder is liquified. Referring to the image of the corroded contact in place, the solder pad is the entire joint as seen at upper right of the image.
I used a little universal solvent and these cleaned right up. I did pick at the spring a little to free larger chunks of the crystalline build up, but for the most part minimal agitation was required.
While the parts were out to wash I did a quick pass on the battery compartment with a wet rag.
Battery door flap back in place just before snapping the rear case half back into place & returning the hardware to its original position.
I'm happy to report the unit works like a champ now. All in all I think the entire span of time spent on this was about a half hour, including stopping to take pictures or reprimand my two year old assistant.