One of the Technics SL1200 mk2 biggest weaknesses are the bearings they are situated vertically between 2 points as in (fig3) these allow the arm to freely move across the record any damage to these will cause the record to skip or even stop the arm moving across altogether.
If you look in (pic1) a small dent in the casing traps the race of balls from turning. this is normally caused by transporting the decks with the counter weight on, If this happens you normally replace the complete arm assembly sold for around $A150.00 pus someone to fit expensive. Most people just loosen the top lock screw and place the bluetac and 5 cent piece. I have now come up with a new improved bearing set higher quality set in a silicon shell guaranteed not to pinch or jam even when you transport with the counter weight on, so if you're a DJ and care about your records just complete a this simple test on your decks check to see if there is any play in the arm just by holding the headshell and moving back and forth feeling for movement. Now make sure the deck is level, Yes you can buy a little spirit level from a hardware shop for a Couple of bucks screw the legs up or down to achieve level from left to right and back to front now with the headshell on turn the counter weight until the arm is balanced (in a floating position) set the anti skate to zero move the arm all the way across to the center spindle, release the arm and turn anti skate knob to 3 the arm should move freely back to the arm rest if it stops halfway across the platter there is a 99% chance you have damaged bearing set . One other problem that i often see is damage to the end of the arm where the counter weight sits as you can see in pic4 (underside) this part is made of plastic, again cause transporting with counterweight on, its funny that I've said many times don't transport with the weight on.. the answer i don't want to lose it ! I recorded reasons for changing arms and 58% was due to pivot bearing pinched or trapped 22% bent chrome arm pipe 13% stylus connector pins and last of all 7% due to jealous girl/boy friends. Hit them where it hurts most. I do believe the reason why djs reverse the counter weight and stick bits and bobs on the head shell is lost faith due to problems in the past, so loads of weight just in case so why not have 6 aspirin for the headache that you may have tomorrow all your doing is wasting money and making styli manufactures rich they state in the operating instruction manual high sensitivity low mass gimbal suspension tone arm ra ra ra this is fine if you buy a deck and stick it in your room and never take it walkabout but today djs are flying around the world with there decks and weighing in at 12.5 kg plus road case they get dropped and abused. Next on the list Contact Pins, iam sure if your a DJ and work in clubs and take your own head shells you would have had the problem of one channel not working or bad earth problems (buzzing) well i found a range of faults that cause this Contact points as seen in (fig1) notice how the pins have gone rusty this is due to the habit of licking the end of the head shell to get a good contact, yes it does work but the acid in your mouth and the presents of different metals and a electrical current cause electrolysis, if you use the original Technics head shell you will never have this problem but if the damage is done you will have to replace the pins, always look for flat clean gold contacts as in fig 2. notice in fig3 that the top 2 pins are pitted the top 2 pins are the positive left and right channels from the coil on the cartridge these 2 pins carry the current to the mixer and are most susceptible to bad contact and damage while were on the point of head shells the reason i say use the original head shell or Technics is most of the others don't have gold connectors mostly chromium plated on brass this is the main cause of corrosion the mixture of a range of metals alloys etc react and attack each other with the presents of moisture acid (spit) so spend the extra on Technics they were made for it. If you want to use groove masters etc try and buy the type that fits to the original head shell i have often had the problem where the pins in the arm have been pushed in and get stuck and found that allot of the all in one head shells ie track master ra ra have gold connectors but are to long and to big as in fig 4 this pushes the pins in and the plastic at the bottom of the connector and causes the plastic to bur in and this traps the pins, fig 2 the Stanton headshell chromium plated no no fig3 Technics head shell notice how the pins come to a point they create a small dent in the connectors in the arm and fit aluminum to aluminum and gold to gold for a perfect connection so if you want carefree DJ sessions stick with the Technics so the next DJ cant get a good connection.
if you are like me and have prized records that you've had for thirty or forty years and would like to keep Them top notch condition try to use as less weight on the Stylus as possible even if the stylus manufacture specs allow for more Happy spinning. .