While I was dismantling an 84 D100 for parts I found a possible replacement for the two rubber flap seals that go on the cowl.
The late model pickups have a similar seal on the passenger/right side cowl behind the fender. They are discontinued 3794032, but at least you can find them in bone yards and they will be in better condition. There is only one, not two on the late models.
Also, the two little nipples that hold them on are different, they are spread out more than the 61-71's but drilling two new holes would be a piece of cake and it does cover the hole.
Mark D.
1968 W200 Sweptline
1969 D100 Utiline
1971 D100 SE Sweptline
1993 D250 Club Cab Sweptline
1986 W250 Cab & Chassis
1978 D300 Sweptline
E. Brookfield, Massachusetts