I suspect your synchro are worn. Adjusting the linkage is more closely related to having issues with it not going into gear due to misalignment
I think you should try red line MTL ( my phones auto correct keeps putting a space between red and line)
If you have to wait to shift when the rpm of the engine trails off significantly, it is likely because the synchro mesh gears are worn.
I will replace mine when the engine comes out
Until then I will just be a bit more cautious shifting and using this special oil really helps.
I take off the left rear wheel for easy access, try to keep the car level if possible, pull the fill plug first (top one, if you're sitting by now exposed gearbox end, where wheel used to be, just rearward of hub and up a bit, get that out, then pull the lower let it drain into something, if you've just driven the car so it's a tad warm it will drain quicker, (inspect backside of plug, magnet will be full of metal "dust" hopefully nothing too chunky, wipe it clean), replace drain plug, pull fill plug, a larger diameter tube, clear plastic (so you can see flow and monitor when it's full), about 1/2" OD so it crams into the fill hole snugly, route tube up into engine bay, funnel, pour in MTL, it will pour easily unlike the gear oil that is super thick when cold, MTL isn't. About 4 quarts will go in there, some overfill a bit, I think I order 5 and use a tad over 4, book says something like 3.5. Make sure the vent is open, very top of 5 speed extension, by wheel hub, little white cap thing, remove grime. Gearbox must breathe or leaks will ensue.
.....mine (with MTL) still rattles in neutral with clutch engaged, bit annoying but I live with it....
I find it easier to jack up the car high using a floor jack on the center-rear pad, lifting both rear wheels and the rear end high. You can also use the factory jack on the left side. (As always, use a jack stand for security as well.)
Then pull the top and bottom plugs as suggested using a standard flat "oil change" plastic pan you can get almost anywhere for a few bucks.
Once the oil is running out... Pull the jack stand and lower the car to the ground to get it ALL out. (Lift the front end??? Lift the right side???)
Oh... Best price I found for 4 quarts... and I have never been able to install MORE than 3.5 quarts in any 5 speed...
Free Shipping too!
http://www.ebay.com/itm/Red-Line-Oi...Parts_Accessories&hash=item5d370b97e2&vxp=mtr
You are gonna LOVE the difference!