[Vwdiesel] High pitched squeal when driving 020 tranny in 5th gear

[ken1]

Me and my 1982 MK1 1.6L NA diesel caddy....
While on my way to Ear, Nose & Throat appointment, I thought I heard a very high pitched squeal, (sort of like a belt slipping on alternator). So, I went faster and sure enough, it got louder. When I slowed down, the squeal got quieter. Then I down shifted to 4th gear and the sound went away, even when I was at same speed and RPM as I was in 5th gear. Never had a 020 5 speed transmission before, but I have read a lot on the forum. My initial thought is "low on transmission oil". I was only about 5 miles from home, so drove back in 4th gear, dashed inside, called Doctor to cancel appointment and send this message. After this, I will change clothes and gather my tranny dipstick from the special tools section and some tranny fluid and cross my fingers. When the oil is low doe 5th gear squeal or whine? Hoping for the best and will update after check and test. Wish me luck. ken  
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1982 caddy 1.6L NA running
1967 convertible bug running
1980 caddy project