I have repaired many this way, using Pirtek MPH 06 hose. I used to keep the hydro barb at the pipe connection, however they are less secure than a brass 3/8 BSP tail. I drill the 5/8 UNF hydro flare nut to 13mm to fit the tail.
I used to get Pirtek to crimp the hoses, but now use 2 Oetiker circle clamps each end.

Edit August 2024:
I previously tapped the bag 1/8 BSP x 3/8" deep, and fitted a SS nipple and 1/8 x 3/8 reducing bush, Loctite 262 the fittings.
I now recommend using 2 Oetiker clamps onto the barb instead. Because I got leak problems when tapping into the bag where the barb was. There's not much metal in there.

Old bags that have dried out over the years are less successful, some crack through the rubber cone at the top. Bags should be stored with glycol antifreeze in them.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Other rubber goods are often stored long term in a bag with talcum powder in it, I bought a serpentine drive belt packed this way.
On car though, it's really just the dust boot that hardens and can crack eventually. But this takes many years. New boots are still available.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I now keep the original barb on the bag by carefully cutting the crimp off with a die grinder.
I then use Pirtek MPH06 hose with 2 Oetiker full circle clamps on both ends.
Tested fine at 300 psi.
I made an offset crimper from a big pair of pliers but you can buy them on eBay.

The Pirtek brass crimp in the top picture looks pretty but it's very thin, i have had one leak when using the original hose end barb. But OK with a 3/8 brass barb fitting.
Use with either the original steel 5/8 UNF nut or a brass oxy hose nut.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.