During Kavkaz 2016, the Russian 58th Army was ordered to reactivate T-62 variants in storage and bring them back up to a standard where they could be used in actual operations and combat.
Russia started supplying T-62Ms to Syria the following year...
During Vostok 2018, units from the Central and Eastern Military Districts were ordered to bring about two companies worth of T-62 tanks out of storage and reactivate them. Those tanks were then transported all the way to the Western Military District using Russian Railways. Work carried on after Vostok until a battalion of tanks had been overhauled. Later on that year, those tanks were also sent to Syria. Some were pressed into combat still bearing Russian camouflage and their "H22-0-0" Russian Rail Transit Markers.
The aim of such exercises were to check Russia's capabilities to fight a total war on the Western front: How long would it take to reactivate old tanks in storage/mothballs in various Russian Military District and what are the best procedures to do so. Additionally, how fast could those units be brought up to the West to reinforce Russian units fighting along its Western borders (the West is almost always the aggressor in Russian wargames). A secondary objective was to supply the SAA with "new" armour to replenish their ranks decimated by years of attrition. Under an agreement between Moscow and Damascus, it is Russia's responsibility to train and equip the SAA.
While the T-62M is an old tank by any standards, it is good enough for the type of war the Syrian Army prosecutes on its soil: After all, it was good enough to prosecute Russia's counter-insurgency operations in the Caucasus until fairly recently!
The story doesn't stop there, however: While the T-62 no longer appears on the Russian Army list of hardware (it was still present on said list in 2020!), teams of mechanics in all military districts are still working on them in order to reactivate them. We are not talking about a large scale operation, here: Only a handful of storage depots and armouries are involved. But it means that men working in those units are regularly practicing the art of overhauling older tanks and returning them back to operational status. This skill is a precious strategic asset for the Russian army: While it currently operates 2850 tanks, Moscow still holds 10,000 older T-72, T-80 and T-90 in reserve! In a modern war of attrition, the winner could probably be the one side that can keep supplying men and hardware to the frontline!
Some of those overhauled tanks end up in Syria. But some seem to be used in Russia itself for the purpose of (logistics) exercises: Tanks are rapidly mobilised, assembled at the nearest Railway Hub and are then moved from one Military District to another. It seems Moscow is upgrading 150 T-62M to a newer higher standard (T-62M3) and that this handful of modernised tanks will remain in that role for the foreseeable future. What remains of T-62 in the Russian inventory will most probably be slowly reactivated and sent to Syria.
So... What does it take to overhaul a tank that has been stored for some time? Well, it depends on how long the tank was left idle, to be honest! The T-62 that were reactivated in the Caucasus in 2016 had barely been in storage for a couple of years. The ones being overhauled in the other Military Districts may have been mothballed for several years longer.
The rust on the body of a tank is usually superficial. Nevertheless, the gun and breach are usually thoroughly checked for corrosion and pitting.
The drivetrain is drained of all fluids and disassembled. The engine is checked for water and dirst ingress. Hydraulic and oil lines are pressurised and tested. All perished seals are replaced. The whole assembly is then cleaned and reassembled.
The electrics/electronics are thoroughly checked but they are fairly resilient in older Soviet (legacy) tanks as connections are usually tin coated against corrosion and oxydation.
Optics and glass are checked for moss, pitting and vitricolous lichens.
KDT Laser Finder and Volna Fire Control Systems are taken out of their crates and checked and dessicated. Luna IR projectors are checked. All corroded parts are cleaned or replaced.
It is hard thorough work and as said above, the longer the tanks have been mothballed, the longer it takes to bring them back to operational status: Russia doesn't have bone dry deserts to store its reserve vehicles. But it seems that on average, a team can bring a T-62 variant back to life inside of 7 working days.