Found this from a forum...  

Title: Re: 3.0 MV6 Fan Belt
Post by Pete Elite on 04. Sep 2009 at 23:36 
--------------------------------------------------------------------------------
Hi, 
   My 96 3.0L Auto with Aircon uses the 93181720 and i would have thought that this should be the one for yours as well :-?.
I got the info. below from my EPC which doesn't even mention belt # 93181720 but instead 93181721 which I've highlighted:-?.
1  BELT,DRIVE,21.36 X 1900 MM,ALTERNATOR (IDENT FK) (NLS.- USE 9118618 OPEL 91126386VAUXHALL)
EXCEPT AIR CONDITIONING X25XE,X30X   1  90409782  13 40 742    
2  BELT,DRIVE,21.36 X 1900 MM,ALTERNATOR (IDENT FW) (NLS.- USE 9118618 OPEL 91126386VAUXHALL)
EXCEPT AIR CONDITIONING X25XE,X30X -W1193599
1  90500228  13 40 614    
4  BELT,DRIVE,21.36 X 1900 MM,ALTERNATOR (IDENT FX) (FOR DELETION OF AIR CONDITIONING PARTS) (FOR VAUXHALL) (NLS.- USE 93181719) X25XE,X30X W1193600-
1  91126386      
7  BELT,DRIVE,21.36 X 2260 MM,ALTERNATOR (FOR JAPAN) (IDENT FX) (NLS.- USE 9118620) (SEE SERVICE INSTRUCTIONS)
USED WITH AIR CONDITIONING X25XE,X30X R1000001-S1059678
1  90500354  13 40 615    
6  BELT,DRIVE,21.36 X 2020 MM,ALTERNATOR (IDENT AC) (USED WITH AIR CONDITIONING) (NLS.- USE 9118620) (EXCEPT VAUXHALL) X25XE,X30X S1059679-X1032987
1  90528761  18 54 728    
6  BELT,DRIVE,21.36 X 2020 MM,ALTERNATOR (IDENT AC) (USED WITH AIR CONDITIONING) (NLS.- USE 91126388) (FOR VAUXHALL) X25XE,X30X S1059679-X1032987
1  90528761  18 54 728    
9  BELT,DRIVE,21.36 X 2020 MM,ALTERNATOR (IDENT FX) (USED WITH AIR CONDITIONING) (FOR VAUXHALL) (NLS.- USE 93181721) X25XE,Y26SE,X30XE,Y32S X1032988-
1  91126388      
10  ROLLER,TENSION (NLS.- USE 90528760) X25XE,X30X   1  90409783  13 40 536    
10  ROLLER,TENSION (NLS.- USE 9202550) X25XE,Y26SE,X30XE,Y32S   1  90528760  13 40 547    
10  ROLLER,TENSION X25XE,Y26SE,X30XE,Y32S   1  9202550  63 40 538    
11  -PULLEY,TENSIONER X25XE,Y26SE,X30XE,Y32S   1  9157962  13 40 512    
12  -SCREW,PULLEY,M10 X 30 X25XE,Y26SE,X30XE,Y32S   1  9157950  13 40 801    
13  -NUT,PULLEY,M10 (NLS.- USE 12992580) X25XE,Y26SE,X30XE,Y32S   1  9157951  13 40 802    
13  -NUT,PULLEY,M10 X25XE,Y26SE,X30XE,Y32S   1  12992580  13 40 832    
14  -COVER,PROTECTION,TENSIONER X25XE,Y26SE,X30XE,Y32S   1  9157963  13 41 667    
         HTH,
               Pete 

.
  PS. It seems to me that both the belts that dbug has mentioned have had the last digit added to by 1 in the EPC that I've shown, Very odd :-?.