ULSD can very much affect seals.. I've seen it happen on older school buses, and have had mechanics tell me they've seen it happen on older equipment of all sorts. the only way out is to rebuild with ULSD compatible materials. pretty much what happens is that the seals have been swelled for so long, the ULSD comes along and shrinks the seal, causing the leak.
here's an excerpt from a document from the nuclear regulatory commission on ULSD and its effects.. I just copied the section on " fuel system leaks"..you can google the information notice number and read the rest of the report.. it's funny - the gov't knows how bad the stuff is, yet still forces it down everyone's throat.
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C.20555-0001
October 12, 2006
NRC INFORMATON NOTICE 2006-22:
NEW ULTRA-LOW-SULFUR DIESEL FUEL OIL COULD ADVERSELY IMPACT DIESEL ENGINE PERFORMANCE
"Fuel System Seal Leaks
Non-nuclear industry operating experience using ULSD shows an increased incidence of fuel system leaks at points where elastomers (O-rings) are used to seal joints, with most leaks occurring at the fuel pump and injectors. The evidence to date suggests the problem is linked to a reduction in the aromatics content of the ULSD, which affects seal swelling, as does seal material and age of the material."
