Old chestnut - arc_very_old_pages?

One of the systems I occasionally support is running 7.31FD3 on Alpha 4.0, and lately they've often had ontape Level-0 backups take 3-1/2 hours (2 or 3 out of every 10) when they normally see 50 minutes. It doesn't sound much but it's impinging on their overnight batches. They're backing up 25Gb or so onto DLT. Thing is, they've got CCFLAGS set to 0x400000 as per the recommended fix for versions above 7.31UC7 so the bug should have been circumvented, yes? I've not been able to get them to run onstat -g ath to look for arc_very_old_pages running yet, that won't happen (dba availability) until next week but in the interim does anyone have any ideas if bug 101062 shows up even with this CCFLAGS setting? Oh, they've still got TAPEBLK set to 64k, I reckon they could lift this to 256 and probably 512. Any recommendations? Ta Malc