Classic/Antique Car Repair: 63 valiant problems, muffler shop, gas consumption

Question
i have a 63 valiant with a slant 6 (170 i think) and it suddenly had problems accelerating and increased gas consumption. oil was also dripping out of the oil fill cap (which is ventilated). i was using the car to drive to work (60 miles) each way 4 days a week because it ran so well and got great gas mileage. during the same time as the other problems, the muffler either imploded or exploded and developed a large hole. i replaced the muffler with a free flowing cherry-bomb type assuming the problem would be fixed but it didn't do much. i brought the car to a local mechanic and he suggested that a valve job was needed. i believed him until i ran into a retired mechanic who insists the problem is a collapsed exhaust pipe. he never saw my car but has worked on many in the past and he says it's a common problem. what do you think?

Answer
Without putting it on an engine analyzer and doing some tests,  I'm only guessing, but I'd sure take it to a muffler shop and have them check that whole system for a restriction, because the old guy is very likely right.  In any case, that's a $50 problem, whereas the valve problem is a $500 problem, so do the easy thing first.  You don't say how many miles are on the engine, but slant 6s should go at least 150,000 miles without any problems - more if it was well cared for (oil changed every 3000 miles or so).  There are few better engines around - so give it a chance to get back to normal.

To find out if it needs a valve job, you can do a compression test, but I'd do the exhaust pipe first!

Dick