Yes, after such a long time you should check it all over before re powering and use - there's less risk of anything expensive happening with the preamp and tuner but after nearly 35 years it's time for a service, they'll sound fantastic afterwards!
As I see it you have three options dependent on your own level of electronics skill
1) Get the excellent refurb kits for each piece from DaDa electronics and install them yourself. These kits are excellent and will upgrade as well as refurbish.
http://www.dadaelectronics.eu/shop/quad-upgrade-kits
2) Have DaDa upgrade and refurbish them for you
http://www.dadaelectronics.eu/prices
3) Quad still service these great amps and tuners - send it all to them in Huntingdon
http://quad-hifi.co.uk/our-story.php?id=19
I hope this helps.
Cheers,
Steve.