This first came to light as a Service Letter in December 2009; see
http://www.robinsonheli.com/srvclib/r44sl36.pdf
As you will see from the Service Letter the replacement bladder tank was then priced at $13,500 and it was to become mandatory at on factory overhauls but no other time limit was specified.
I have heard it mentioned that the new Service Bulletin with a compliance time limit attached to it may be an effort by RHC to stave off an AD from the FAA. The almost 50% discount offered in the SB would tend to support this view as it follows similar pattern to earlier R44 issues such as the mandatory blade replacement on early R44 Astros.
As mentioned on a related thread there are about 5,000 R44s in service around the world. Having to produce an extra 5,000 sets of tanks would be a major production effort.
I have a question to ppruners on this:-
Will the bladder tanks have to be replaced at the the standard 12 year rebuild?
Bladder tanks are not uncommon if fixed wing aircraft neither are bladder tank leaks mainly due to age related degradation.
No word, as yet, from RHC about a similar mod on R22s. Instead bacck in 2006 RHC suggested that the occupants wear Nomex Flight Suits and Helmets;
http://www.robinsonheli.com/srvclib/r44sn40.pdf
although to be fair this same Safety Notice did also apply to R44s.