Not sure 94 compared to 91 will do much for the engine but it doesn't hurt. Running through injector cleaner every 3 months probably has the same effect. I personally use 99.9% iso propyl alcohol as an additive every once a while (plus premium is not available where I usually drive to work).
Oil and filter are easy to change on mk3 gti's. Actually you don't even need to jack it up if you got a flat drain container (I use a 6 liter drain container that's only 10-12cm high. With a well WARM engine, just turn you steering wheel fully to the right and you can reach the drain plug (use a 19mm SOCKET to undo, does save you from ruining the head with a spanner). Just loosen with the socket, then slowly undo by hand, but keep pressing it into the thread, once you feel it is undone then take the screw out in a fast move, so the oil misses you and goes only into the container.
Just leave to bleed out. Oil filter is easy then, can be undone by hand (unless an idiot tightened it up too much and hasn't used any oil or grease on the seal, then you need a tri-clamp thing). Once the old filer is off make sure the gasket does not stick on the block and mop up leaking oil around the filter flange, apply high temp grease or otherwise engine oil to the seal and screw new filter on.
The replace the copper ring on the oil sump plug (14x20x1.5mm) and replace the plug, don't overtighten the screw. Then fill in 3.5 liters, start engine and allow for the oil warning light to go off - this should take no longer than 15 seconds, otherwise shut it down! Then wait a minute and check level on dipstick and top up to just below max. Then run engine again and check for any leaks around the oil drain plug and the filter.
Easy job and you're done in half an hour.
Your speedo not working is most likely a bad contact or soldering in the speedo, (does the mileage and clock work?). Just take it out and try if unplugging and plugging it back in again helps. It's easy - if you have an adjustable steering wheel column just put it on the very bottom position, otherwise remove the column cover (two Philipshead screws at it's bottom) then only the light switch and a plastic trim next the the speedo at left an right need to come out. Trim just unclips, light switch needs to be removed by inserting a long tool (feeler gauge could work) and move it to the left or right... there is a pin inside that unlocks it temporarily so keep it in place, then pull light switch out. It doesnt need to be unplugged but if you do its not a big thing to put connector back in.
You'll then see the philips screws, take them out and remove the dash frame. Then next to speedo are two more philips screws, take them out, lift the speedo and undo one or in CA probably two connectors. Then you can take it out....
If plugging it in again doesn't solve it let me know, then it's something else at fault (maybe cold solders on the board or a blown voltage regulator). All things that can be fixed with not too much effort.
Cheers
M
