Hi Daniel,
My .308 M55 is over 30 years old and as good as new. They are lovely rifles, made at the original Tikka factory (ie pre-Sako etc). The early ones, like mine, had a rounded forend then, in about 1980, they changed it to a cut-off, angled forend. The deluxe version has a rosewood tip with ivory banding. They have a lovely swell in the palm grip but only if you are right-handed! It was replaced by the 595 in the late '80s, I think, then Sako bought Tikka and harmonised production: then Beretta bought the lot and introduced modern cost-engineering. The rest, as they say, is history. I won't get into the T3 versus old Tikka debate - the T3 is a good rifle - but "original" Tikkas in good condition are a different rifle altogether and worth finding and taking a pride in IMHO.
They were designed for cold climates and had a large, plastic-covered bolt handle, which can strike a wide, low-mounted scope, so beware. It's fine with a 4x32 - 6x42 etc. They are very well made indeed, very accurate and reliable in the most extreme conditions, which is what they were built for. But be warned that magazines are as rare as hens' teeth! If it's a good one, go for it ...
Incidentally, UK and Australian special forces used the Tikka M55 in 22-250 as their urban sniper rifle in the early-mid '80s.
Hope this helps,
Graeme