I'd like to thank everyone for appreciating with such nice words. 
Hmmm... The best way is to give a call to HEC. I am sure they'll ask you to get it re-attested as a part of the stamp is on the ticket. So if you've done it before, it won't be difficult for you to get it done again. However, you may ask them this time and they make you go through an easier process with less documentation.
OCS is reliable. Many have used their services for attestation purposes. If you are not in a hurry, you may use its services.
For the third part of your query, I've mentioned in that for such attestations, there is an authorized agent in almost every big city. If you can't find it in Lahore, you may come to Islamabad for a day and handover your documents to SASHA in Libra Market aka Khadda Market in G-7. You can search their contact no. online. Do give them a call to confirm the documents required, their timings and the charges. Once you handover your documents to them, you'll have an option to get it couriered to you after attestation.