Hi Adam,
To be honest, no. You can pick up a brand new Canon EF 50mm f/1.8 MKII for about £80 brand new and cheaper 2nd hand on eBay. I'd personally prefer to spend another £30-£50 and get an EF lens that is renowned for its image quality. If the FD lens is in good condition, you could always sell it along with the AV-1 and put the money towards the EF version. Alternatively keep it and practise some good ol' fashioned film photography.
As for the Sun lens, its a cheap 3rd party lens, that in all likelihood, gives average quality results. Stripping a lens down is no easy task and unless you have the right tools for the job, coupled with the know how, you'll end up scratching the elements, damaging the coatings, putting them back in the wrong way round, etc. If the lens has a helical thread, its very easy to reattach the barrel in an incorrect position. The cost of having the lens stripped down and serviced would probably cost close to 5 times what the lens is worth.
Save your money and put it towards some better gear