Distributor cap - quickly failed

good afternoon,
I replaced my damaged distributor cap less than 1000 miles ago (probably less than 500 miles) with a new Bosch one, albeit over a year ago. Recently the car started to miss fire and run badly and due to lack of time..... anyway it would not start today so I grabbed an old cap and leads I had salvaged of an old wreck and swapped them over. I was very dismayed at the Bosch one as it had completely fallen apart in various places !!!!! The new / old one worked of the bat. Now when I was in there it’s clear there is an oil leak from the seal behind the distributor cap.... is this the camshaft ....... and is it the same seal as the far side as I have some spares ...... or at least I hope so...

Question - do you drill two holes in the old seal to remove ? and just clean up and push new ones in ?
- Are they the same at both ends - will the spares I have work ? Thanks for any help. Col

Did you replace the rotor arm too?

Yes the old one was well cooked by the look of it, all very disappointing but I had been warned on this forum not to get my hopes up with aftermarket cap.

Obviously I want to get the oil seal done ASAP but wanted to make sure it was a simple job.......

Ok really struggling to find the part number for the oil seal behind the distributor cap any help would be really appreciated, spent an hour on the net and in manual but not getting anywhere.