.1.3.6.1.4.1.3076.2.1.2.22.1.59 is the correct object here. I tried it on one of VPN 3030 boxes and it shows the correct value:
For example, on the VPN Menu, it shows:
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Up For 69:19:47
Up Since 12/14/2002 13:05:23
RAM Size: 256 MB <---- !!!!!
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And polling using the above OID, give the same result :
% snmpwalk public .1.3.6.1.4.1.3076.2.1.2.22.1.59
enterprises.3076.2.1.2.22.1.59.0 = 256