Hollis is recalling Explorer counterlungs due to a leaking issue caused by weak welding around the retainer fitting.
 
Here is the official press release:
Discontinue use of your Explorer until new counterlungs are installed. Continued use of the original parts could lead to flooding of the counterlungs, Pre-Dive Check failures, and possible drowning.
We have received some counterlungs back due to leaking. We have traced this problem back to one production lot of counterlungs that had weak welds around the retainer fitting. Affected counterlungs can develop leaks over time. Explorers within the serial number range provided below are the only units shipped with these counterlungs. We will send send a free pair of counterlungs to owners of units within the serial number range below. Owners of effected units are asked to complete the return form found here and return it and the cut swatches from the defective counterlungs to Hollis Customer Service.
Serial Number Range:
1002.1207.1111, 1002.1307.1101 – 1002.1307.1154, …